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 $92.56   11.851%   $103.5293   $103.53   $103.55   $103.50  
  Purchase #2 $179.53   9.450%   $196.4956   $196.50   $196.50   $196.50  
  Purchase #3 $74.73   10.104%   $82.2807   $82.28   $82.30   $82.30  
  Purchase #4 $190.63   11.185%   $211.952   $211.95   $211.95   $212.00  
  Purchase #5 $6.40   8.551%   $6.9473   $6.95   $6.95   $6.90  
  Purchase #6 $25.40   7.608%   $27.3324   $27.33   $27.35   $27.30  
  Purchase #7 $183.29   13.303%   $207.6731   $207.67   $207.65   $207.70  
  7 purchase totals = $752.54       $836.2104   $836.21   $836.25   $836.20