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 $119.64   6.708%   $127.6655   $127.67   $127.65   $127.70  
  Purchase #2 $248.33   4.739%   $260.0984   $260.10   $260.10   $260.10  
  Purchase #3 $132.26   9.448%   $144.7559   $144.76   $144.75   $144.80  
  Purchase #4 $155.54   7.858%   $167.7623   $167.76   $167.75   $167.80  
  Purchase #5 $121.32   11.622%   $135.4198   $135.42   $135.40   $135.40  
  Purchase #6 $234.29   6.532%   $249.5938   $249.59   $249.60   $249.60  
  Purchase #7 $71.91   4.246%   $74.9633   $74.96   $74.95   $75.00  
  7 purchase totals = $1,083.29       $1,160.2590   $1,160.26   $1,160.20   $1,160.40