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 $234.39   9.237%   $256.0406   $256.04   $256.05   $256.00  
  Purchase #2 $38.45   6.570%   $40.9762   $40.98   $41.00   $41.00  
  Purchase #3 $139.45   10.362%   $153.8998   $153.90   $153.90   $153.90  
  Purchase #4 $199.28   11.853%   $222.9007   $222.90   $222.90   $222.90  
  Purchase #5 $191.45   5.240%   $201.482   $201.48   $201.50   $201.50  
  Purchase #6 $167.96   6.394%   $178.6994   $178.70   $178.70   $178.70  
  Purchase #7 $221.50   11.787%   $247.6082   $247.61   $247.60   $247.60  
  7 purchase totals = $1,192.48       $1,301.6069   $1,301.61   $1,301.65   $1,301.60