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 $71.49   5.216%   $75.2189   $75.22   $75.20   $75.20  
  Purchase #2 $53.58   3.586%   $55.5014   $55.50   $55.50   $55.50  
  Purchase #3 $238.52   9.704%   $261.666   $261.67   $261.65   $261.70  
  Purchase #4 $86.46   11.110%   $96.0657   $96.07   $96.05   $96.10  
  Purchase #5 $78.82   7.809%   $84.9751   $84.98   $85.00   $85.00  
  Purchase #6 $153.26   12.451%   $172.3424   $172.34   $172.35   $172.30  
  Purchase #7 $185.97   13.195%   $210.5087   $210.51   $210.50   $210.50  
  7 purchase totals = $868.10       $956.2782   $956.29   $956.25   $956.30