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 $236.61   8.518%   $256.7644   $256.76   $256.75   $256.80  
  Purchase #2 $229.58   7.305%   $246.3508   $246.35   $246.35   $246.40  
  Purchase #3 $210.39   11.536%   $234.6606   $234.66   $234.65   $234.70  
  Purchase #4 $61.84   10.355%   $68.2435   $68.24   $68.25   $68.20  
  Purchase #5 $9.37   8.221%   $10.1403   $10.14   $10.15   $10.10  
  Purchase #6 $108.93   13.198%   $123.3066   $123.31   $123.30   $123.30  
  Purchase #7 $98.41   8.849%   $107.1183   $107.12   $107.10   $107.10  
  7 purchase totals = $955.13       $1,046.5845   $1,046.58   $1,046.55   $1,046.60