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 $202.38   4.378%   $211.2402   $211.24   $211.25   $211.20  
  Purchase #2 $63.45   11.192%   $70.5513   $70.55   $70.55   $70.60  
  Purchase #3 $23.49   5.262%   $24.726   $24.73   $24.75   $24.70  
  Purchase #4 $177.40   12.802%   $200.1107   $200.11   $200.10   $200.10  
  Purchase #5 $119.45   4.671%   $125.0295   $125.03   $125.05   $125.00  
  Purchase #6 $178.51   10.295%   $196.8876   $196.89   $196.90   $196.90  
  Purchase #7 $87.49   12.473%   $98.4026   $98.40   $98.40   $98.40  
  7 purchase totals = $852.17       $926.9479   $926.95   $927.00   $926.90