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 $67.53   13.383%   $76.5675   $76.57   $76.55   $76.60  
  Purchase #2 $71.53   6.204%   $75.9677   $75.97   $75.95   $76.00  
  Purchase #3 $216.26   8.348%   $234.3134   $234.31   $234.30   $234.30  
  Purchase #4 $140.61   10.349%   $155.1617   $155.16   $155.15   $155.20  
  Purchase #5 $121.67   6.696%   $129.817   $129.82   $129.80   $129.80  
  Purchase #6 $5.96   4.751%   $6.2432   $6.24   $6.25   $6.20  
  Purchase #7 $247.85   3.210%   $255.806   $255.81   $255.80   $255.80  
  7 purchase totals = $871.41       $933.8765   $933.88   $933.80   $933.90