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 $29.39   13.246%   $33.283   $33.28   $33.30   $33.30  
  Purchase #2 $65.50   12.700%   $73.8185   $73.82   $73.80   $73.80  
  Purchase #3 $198.97   4.312%   $207.5496   $207.55   $207.55   $207.50  
  Purchase #4 $84.50   12.593%   $95.1411   $95.14   $95.15   $95.10  
  Purchase #5 $93.72   5.169%   $98.5644   $98.56   $98.55   $98.60  
  Purchase #6 $185.35   8.717%   $201.507   $201.51   $201.50   $201.50  
  Purchase #7 $66.42   7.642%   $71.4958   $71.50   $71.50   $71.50  
  7 purchase totals = $723.85       $781.3594   $781.36   $781.35   $781.30