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 $34.31   5.633%   $36.2427   $36.24   $36.25   $36.20  
  Purchase #2 $10.79   3.352%   $11.1517   $11.15   $11.15   $11.20  
  Purchase #3 $224.88   11.534%   $250.8177   $250.82   $250.80   $250.80  
  Purchase #4 $82.37   13.514%   $93.5015   $93.50   $93.50   $93.50  
  Purchase #5 $205.48   6.354%   $218.5362   $218.54   $218.55   $218.50  
  Purchase #6 $65.37   6.109%   $69.3635   $69.36   $69.35   $69.40  
  Purchase #7 $210.45   7.584%   $226.4105   $226.41   $226.40   $226.40  
  7 purchase totals = $833.65       $906.0238   $906.02   $906.00   $906.00