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 $70.76   8.181%   $76.5489   $76.55   $76.55   $76.50  
  Purchase #2 $216.83   6.562%   $231.0584   $231.06   $231.05   $231.10  
  Purchase #3 $159.59   6.157%   $169.416   $169.42   $169.40   $169.40  
  Purchase #4 $57.48   9.801%   $63.1136   $63.11   $63.10   $63.10  
  Purchase #5 $56.92   9.199%   $62.1561   $62.16   $62.15   $62.20  
  Purchase #6 $196.25   7.147%   $210.276   $210.28   $210.30   $210.30  
  Purchase #7 $110.84   8.191%   $119.9189   $119.92   $119.90   $119.90  
  7 purchase totals = $868.67       $932.4879   $932.50   $932.45   $932.50