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 $59.40   11.348%   $66.1407   $66.14   $66.15   $66.10  
  Purchase #2 $30.36   9.491%   $33.2415   $33.24   $33.25   $33.20  
  Purchase #3 $222.31   4.687%   $232.7297   $232.73   $232.75   $232.70  
  Purchase #4 $86.36   13.855%   $98.3252   $98.33   $98.35   $98.30  
  Purchase #5 $108.92   3.478%   $112.7082   $112.71   $112.70   $112.70  
  Purchase #6 $144.82   7.131%   $155.1471   $155.15   $155.15   $155.10  
  Purchase #7 $70.73   6.793%   $75.5347   $75.53   $75.55   $75.50  
  7 purchase totals = $722.90       $773.8271   $773.83   $773.90   $773.60