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 $238.31   11.195%   $264.9888   $264.99   $265.00   $265.00  
  Purchase #2 $247.53   8.148%   $267.6987   $267.70   $267.70   $267.70  
  Purchase #3 $248.93   4.526%   $260.1966   $260.20   $260.20   $260.20  
  Purchase #4 $83.45   11.125%   $92.7338   $92.73   $92.75   $92.70  
  Purchase #5 $173.44   3.131%   $178.8704   $178.87   $178.85   $178.90  
  Purchase #6 $150.48   7.505%   $161.7735   $161.77   $161.75   $161.80  
  Purchase #7 $193.28   7.194%   $207.1846   $207.18   $207.20   $207.20  
  7 purchase totals = $1,335.42       $1,433.4464   $1,433.44   $1,433.45   $1,433.50