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 $174.91   3.438%   $180.9234   $180.92   $180.90   $180.90  
  Purchase #2 $7.28   3.436%   $7.5301   $7.53   $7.55   $7.50  
  Purchase #3 $23.74   13.681%   $26.9879   $26.99   $27.00   $27.00  
  Purchase #4 $23.61   13.317%   $26.7541   $26.75   $26.75   $26.80  
  Purchase #5 $137.48   8.768%   $149.5342   $149.53   $149.55   $149.50  
  Purchase #6 $204.81   7.295%   $219.7509   $219.75   $219.75   $219.80  
  Purchase #7 $190.30   10.303%   $209.9066   $209.91   $209.90   $209.90  
  7 purchase totals = $762.13       $821.3872   $821.38   $821.40   $821.40