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 $242.49   8.863%   $263.9819   $263.98   $264.00   $264.00  
  Purchase #2 $74.36   9.652%   $81.5372   $81.54   $81.55   $81.50  
  Purchase #3 $243.55   7.464%   $261.7286   $261.73   $261.75   $261.70  
  Purchase #4 $211.72   11.197%   $235.4263   $235.43   $235.45   $235.40  
  Purchase #5 $242.61   10.596%   $268.317   $268.32   $268.30   $268.30  
  Purchase #6 $41.91   11.740%   $46.8302   $46.83   $46.85   $46.80  
  Purchase #7 $187.51   8.650%   $203.7296   $203.73   $203.75   $203.70  
  7 purchase totals = $1,244.15       $1,361.5508   $1,361.56   $1,361.65   $1,361.40