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 $156.58   10.680%   $173.3027   $173.30   $173.30   $173.30  
  Purchase #2 $175.95   8.383%   $190.6999   $190.70   $190.70   $190.70  
  Purchase #3 $47.71   7.657%   $51.3632   $51.36   $51.35   $51.40  
  Purchase #4 $111.33   13.151%   $125.971   $125.97   $125.95   $126.00  
  Purchase #5 $165.32   12.873%   $186.6016   $186.60   $186.60   $186.60  
  Purchase #6 $158.94   12.182%   $178.3021   $178.30   $178.30   $178.30  
  Purchase #7 $119.70   13.163%   $135.4561   $135.46   $135.45   $135.50  
  7 purchase totals = $935.53       $1,041.6966   $1,041.69   $1,041.65   $1,041.80