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 $125.37   8.772%   $136.3675   $136.37   $136.35   $136.40  
  Purchase #2 $201.45   12.463%   $226.5567   $226.56   $226.55   $226.60  
  Purchase #3 $194.41   4.619%   $203.3898   $203.39   $203.40   $203.40  
  Purchase #4 $112.93   5.257%   $118.8667   $118.87   $118.85   $118.90  
  Purchase #5 $182.54   6.360%   $194.1495   $194.15   $194.15   $194.10  
  Purchase #6 $68.77   10.872%   $76.2467   $76.25   $76.25   $76.20  
  Purchase #7 $64.73   4.316%   $67.5237   $67.52   $67.50   $67.50  
  7 purchase totals = $950.20       $1,023.1006   $1,023.11   $1,023.05   $1,023.10