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 $156.70   12.410%   $176.1465   $176.15   $176.15   $176.10  
  Purchase #2 $164.29   12.146%   $184.2447   $184.24   $184.25   $184.20  
  Purchase #3 $227.32   8.404%   $246.424   $246.42   $246.40   $246.40  
  Purchase #4 $73.54   11.733%   $82.1684   $82.17   $82.15   $82.20  
  Purchase #5 $62.73   12.506%   $70.575   $70.58   $70.60   $70.60  
  Purchase #6 $41.32   13.667%   $46.9672   $46.97   $46.95   $47.00  
  Purchase #7 $27.95   9.354%   $30.5644   $30.56   $30.55   $30.60  
  7 purchase totals = $753.85       $837.0902   $837.09   $837.05   $837.10