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 $232.69   13.698%   $264.5639   $264.56   $264.55   $264.60  
  Purchase #2 $114.33   3.522%   $118.3567   $118.36   $118.35   $118.40  
  Purchase #3 $101.37   7.240%   $108.7092   $108.71   $108.70   $108.70  
  Purchase #4 $188.41   10.215%   $207.6561   $207.66   $207.65   $207.70  
  Purchase #5 $189.95   12.674%   $214.0243   $214.02   $214.00   $214.00  
  Purchase #6 $58.41   9.589%   $64.0109   $64.01   $64.00   $64.00  
  Purchase #7 $10.43   9.148%   $11.3841   $11.38   $11.40   $11.40  
  7 purchase totals = $895.59       $988.7052   $988.70   $988.65   $988.80