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 $218.35   12.622%   $245.9101   $245.91   $245.90   $245.90  
  Purchase #2 $88.39   3.338%   $91.3405   $91.34   $91.35   $91.30  
  Purchase #3 $243.69   11.760%   $272.3479   $272.35   $272.35   $272.30  
  Purchase #4 $172.30   13.776%   $196.036   $196.04   $196.05   $196.00  
  Purchase #5 $26.34   9.842%   $28.9324   $28.93   $28.95   $28.90  
  Purchase #6 $34.84   4.736%   $36.49   $36.49   $36.50   $36.50  
  Purchase #7 $84.42   11.748%   $94.3377   $94.34   $94.35   $94.30  
  7 purchase totals = $868.33       $965.3946   $965.40   $965.45   $965.20