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 $42.68   4.501%   $44.601   $44.60   $44.60   $44.60  
  Purchase #2 $191.43   3.393%   $197.9252   $197.93   $197.95   $197.90  
  Purchase #3 $150.48   11.340%   $167.5444   $167.54   $167.55   $167.50  
  Purchase #4 $72.79   5.147%   $76.5365   $76.54   $76.55   $76.50  
  Purchase #5 $93.40   12.240%   $104.8322   $104.83   $104.85   $104.80  
  Purchase #6 $15.77   7.362%   $16.931   $16.93   $16.95   $16.90  
  Purchase #7 $56.87   5.232%   $59.8454   $59.85   $59.85   $59.80  
  7 purchase totals = $623.42       $668.2157   $668.22   $668.30   $668.00