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 $226.63   7.474%   $243.5683   $243.57   $243.55   $243.60  
  Purchase #2 $188.63   10.723%   $208.8568   $208.86   $208.85   $208.90  
  Purchase #3 $45.95   12.268%   $51.5871   $51.59   $51.60   $51.60  
  Purchase #4 $164.27   8.607%   $178.4087   $178.41   $178.40   $178.40  
  Purchase #5 $58.25   5.610%   $61.5178   $61.52   $61.50   $61.50  
  Purchase #6 $124.37   8.714%   $135.2076   $135.21   $135.20   $135.20  
  Purchase #7 $15.35   6.279%   $16.3138   $16.31   $16.30   $16.30  
  7 purchase totals = $823.45       $895.4601   $895.47   $895.40   $895.50