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 $105.44   13.122%   $119.2758   $119.28   $119.30   $119.30  
  Purchase #2 $104.45   12.276%   $117.2723   $117.27   $117.25   $117.30  
  Purchase #3 $166.33   5.233%   $175.034   $175.03   $175.05   $175.00  
  Purchase #4 $170.55   12.334%   $191.5856   $191.59   $191.60   $191.60  
  Purchase #5 $67.42   13.242%   $76.3478   $76.35   $76.35   $76.30  
  Purchase #6 $94.57   6.819%   $101.0187   $101.02   $101.00   $101.00  
  Purchase #7 $187.82   9.562%   $205.7793   $205.78   $205.80   $205.80  
  7 purchase totals = $896.58       $986.3135   $986.32   $986.35   $986.30