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 $50.52   5.526%   $53.3117   $53.31   $53.30   $53.30  
  Purchase #2 $234.43   13.873%   $266.9525   $266.95   $266.95   $267.00  
  Purchase #3 $13.65   10.630%   $15.101   $15.10   $15.10   $15.10  
  Purchase #4 $94.34   6.617%   $100.5825   $100.58   $100.60   $100.60  
  Purchase #5 $216.31   12.537%   $243.4288   $243.43   $243.45   $243.40  
  Purchase #6 $73.80   4.303%   $76.9756   $76.98   $77.00   $77.00  
  Purchase #7 $8.69   3.428%   $8.9879   $8.99   $9.00   $9.00  
  7 purchase totals = $691.74       $765.3400   $765.34   $765.40   $765.40