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 $59.70   12.215%   $66.9924   $66.99   $67.00   $67.00  
  Purchase #2 $32.91   6.597%   $35.0811   $35.08   $35.10   $35.10  
  Purchase #3 $159.92   5.404%   $168.5621   $168.56   $168.55   $168.60  
  Purchase #4 $222.88   3.734%   $231.2023   $231.20   $231.20   $231.20  
  Purchase #5 $48.82   10.346%   $53.8709   $53.87   $53.85   $53.90  
  Purchase #6 $164.78   6.699%   $175.8186   $175.82   $175.80   $175.80  
  Purchase #7 $25.75   10.417%   $28.4324   $28.43   $28.45   $28.40  
  7 purchase totals = $714.76       $759.9598   $759.95   $759.95   $760.00