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 $78.82   10.606%   $87.1796   $87.18   $87.20   $87.20  
  Purchase #2 $206.61   3.868%   $214.6017   $214.60   $214.60   $214.60  
  Purchase #3 $101.72   10.479%   $112.3792   $112.38   $112.40   $112.40  
  Purchase #4 $24.48   7.746%   $26.3762   $26.38   $26.40   $26.40  
  Purchase #5 $204.47   8.439%   $221.7252   $221.73   $221.75   $221.70  
  Purchase #6 $70.60   4.249%   $73.5998   $73.60   $73.60   $73.60  
  Purchase #7 $106.42   10.427%   $117.5164   $117.52   $117.50   $117.50  
  7 purchase totals = $793.12       $853.3781   $853.39   $853.45   $853.40