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 $56.93   9.676%   $62.4385   $62.44   $62.45   $62.40  
  Purchase #2 $42.41   5.575%   $44.7744   $44.77   $44.75   $44.80  
  Purchase #3 $125.30   5.377%   $132.0374   $132.04   $132.05   $132.00  
  Purchase #4 $244.31   11.563%   $272.5596   $272.56   $272.55   $272.60  
  Purchase #5 $138.37   12.201%   $155.2525   $155.25   $155.25   $155.30  
  Purchase #6 $68.67   5.294%   $72.3054   $72.31   $72.30   $72.30  
  Purchase #7 $56.74   13.313%   $64.2938   $64.29   $64.30   $64.30  
  7 purchase totals = $732.73       $803.6616   $803.66   $803.65   $803.70