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 $69.67   5.733%   $73.6642   $73.66   $73.65   $73.70  
  Purchase #2 $241.68   8.277%   $261.6839   $261.68   $261.70   $261.70  
  Purchase #3 $88.96   8.247%   $96.2965   $96.30   $96.30   $96.30  
  Purchase #4 $110.54   5.693%   $116.833   $116.83   $116.85   $116.80  
  Purchase #5 $116.94   8.310%   $126.6577   $126.66   $126.65   $126.70  
  Purchase #6 $43.46   7.320%   $46.6413   $46.64   $46.65   $46.60  
  Purchase #7 $118.30   7.818%   $127.5487   $127.55   $127.55   $127.50  
  7 purchase totals = $789.55       $849.3253   $849.32   $849.35   $849.30