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 $237.87   11.519%   $265.2702   $265.27   $265.25   $265.30  
  Purchase #2 $222.61   8.496%   $241.5229   $241.52   $241.50   $241.50  
  Purchase #3 $214.99   7.816%   $231.7936   $231.79   $231.80   $231.80  
  Purchase #4 $173.26   12.346%   $194.6507   $194.65   $194.65   $194.70  
  Purchase #5 $18.37   7.609%   $19.7678   $19.77   $19.75   $19.80  
  Purchase #6 $200.82   3.656%   $208.162   $208.16   $208.15   $208.20  
  Purchase #7 $174.63   6.613%   $186.1783   $186.18   $186.20   $186.20  
  7 purchase totals = $1,242.55       $1,347.3455   $1,347.34   $1,347.30   $1,347.50