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 $201.29   12.702%   $226.8579   $226.86   $226.85   $226.90  
  Purchase #2 $116.26   8.174%   $125.7631   $125.76   $125.75   $125.80  
  Purchase #3 $128.75   13.148%   $145.6781   $145.68   $145.70   $145.70  
  Purchase #4 $92.31   9.118%   $100.7268   $100.73   $100.75   $100.70  
  Purchase #5 $34.41   5.509%   $36.3056   $36.31   $36.30   $36.30  
  Purchase #6 $16.99   10.189%   $18.7211   $18.72   $18.70   $18.70  
  Purchase #7 $107.60   3.121%   $110.9582   $110.96   $110.95   $111.00  
  7 purchase totals = $697.61       $765.0108   $765.02   $765.00   $765.10