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 $210.57   8.524%   $228.519   $228.52   $228.50   $228.50  
  Purchase #2 $44.35   8.759%   $48.2346   $48.23   $48.25   $48.20  
  Purchase #3 $95.31   11.252%   $106.0343   $106.03   $106.05   $106.00  
  Purchase #4 $65.54   12.571%   $73.779   $73.78   $73.80   $73.80  
  Purchase #5 $204.95   13.725%   $233.0794   $233.08   $233.10   $233.10  
  Purchase #6 $78.41   8.214%   $84.8506   $84.85   $84.85   $84.90  
  Purchase #7 $48.39   8.243%   $52.3788   $52.38   $52.40   $52.40  
  7 purchase totals = $747.52       $826.8757   $826.87   $826.95   $826.90