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 $231.69   7.456%   $248.9648   $248.96   $248.95   $249.00  
  Purchase #2 $92.26   3.170%   $95.1846   $95.18   $95.20   $95.20  
  Purchase #3 $197.40   11.624%   $220.3458   $220.35   $220.35   $220.30  
  Purchase #4 $184.89   5.528%   $195.1107   $195.11   $195.10   $195.10  
  Purchase #5 $15.50   11.421%   $17.2703   $17.27   $17.25   $17.30  
  Purchase #6 $63.80   11.660%   $71.2391   $71.24   $71.25   $71.20  
  Purchase #7 $105.74   9.140%   $115.4046   $115.40   $115.40   $115.40  
  7 purchase totals = $891.28       $963.5199   $963.51   $963.50   $963.50