Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $216.88   12.206%   $243.3524   $243.35   $243.35   $243.40  
  Purchase #2 $205.40   11.812%   $229.6618   $229.66   $229.65   $229.70  
  Purchase #3 $160.85   8.874%   $175.1238   $175.12   $175.10   $175.10  
  Purchase #4 $237.42   7.491%   $255.2051   $255.21   $255.20   $255.20  
  Purchase #5 $158.25   11.752%   $176.8475   $176.85   $176.85   $176.80  
  Purchase #6 $239.97   11.311%   $267.113   $267.11   $267.10   $267.10  
  Purchase #7 $201.90   12.191%   $226.5136   $226.51   $226.50   $226.50  
  7 purchase totals = $1,420.67       $1,573.8172   $1,573.81   $1,573.75   $1,573.80