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 $40.72   6.455%   $43.3485   $43.35   $43.35   $43.30  
  Purchase #2 $89.28   4.861%   $93.6199   $93.62   $93.60   $93.60  
  Purchase #3 $69.52   13.248%   $78.73   $78.73   $78.75   $78.70  
  Purchase #4 $151.42   12.651%   $170.5761   $170.58   $170.60   $170.60  
  Purchase #5 $88.49   5.320%   $93.1977   $93.20   $93.20   $93.20  
  Purchase #6 $170.77   10.243%   $188.262   $188.26   $188.25   $188.30  
  Purchase #7 $50.74   13.832%   $57.7584   $57.76   $57.75   $57.80  
  7 purchase totals = $660.94       $725.4926   $725.50   $725.50   $725.50