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 $112.32   12.281%   $126.114   $126.11   $126.10   $126.10  
  Purchase #2 $146.25   5.194%   $153.8462   $153.85   $153.85   $153.80  
  Purchase #3 $20.67   9.137%   $22.5586   $22.56   $22.55   $22.60  
  Purchase #4 $244.62   6.802%   $261.2591   $261.26   $261.25   $261.30  
  Purchase #5 $233.77   9.732%   $256.5205   $256.52   $256.50   $256.50  
  Purchase #6 $122.42   5.350%   $128.9695   $128.97   $128.95   $129.00  
  Purchase #7 $40.30   12.285%   $45.2509   $45.25   $45.25   $45.30  
  7 purchase totals = $920.35       $994.5188   $994.52   $994.45   $994.60