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 $23.49   9.618%   $25.7493   $25.75   $25.75   $25.70  
  Purchase #2 $35.83   12.642%   $40.3596   $40.36   $40.35   $40.40  
  Purchase #3 $53.98   11.642%   $60.2644   $60.26   $60.25   $60.30  
  Purchase #4 $245.73   11.157%   $273.1461   $273.15   $273.15   $273.10  
  Purchase #5 $102.99   8.226%   $111.462   $111.46   $111.45   $111.50  
  Purchase #6 $97.48   8.749%   $106.0085   $106.01   $106.00   $106.00  
  Purchase #7 $92.98   8.469%   $100.8545   $100.85   $100.85   $100.90  
  7 purchase totals = $652.48       $717.8444   $717.84   $717.80   $717.90