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 $223.97   12.207%   $251.31   $251.31   $251.30   $251.30  
  Purchase #2 $227.78   8.506%   $247.155   $247.16   $247.15   $247.20  
  Purchase #3 $105.76   11.475%   $117.896   $117.90   $117.90   $117.90  
  Purchase #4 $142.54   11.545%   $158.9962   $159.00   $159.00   $159.00  
  Purchase #5 $69.38   7.595%   $74.6494   $74.65   $74.65   $74.60  
  Purchase #6 $116.30   4.479%   $121.5091   $121.51   $121.50   $121.50  
  Purchase #7 $58.72   6.491%   $62.5315   $62.53   $62.55   $62.50  
  7 purchase totals = $944.45       $1,034.0472   $1,034.06   $1,034.05   $1,034.00