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 $224.40   12.602%   $252.6789   $252.68   $252.70   $252.70  
  Purchase #2 $27.77   3.413%   $28.7178   $28.72   $28.70   $28.70  
  Purchase #3 $60.37   8.159%   $65.2956   $65.30   $65.30   $65.30  
  Purchase #4 $88.65   4.174%   $92.3503   $92.35   $92.35   $92.40  
  Purchase #5 $101.90   10.597%   $112.6983   $112.70   $112.70   $112.70  
  Purchase #6 $178.76   13.370%   $202.6602   $202.66   $202.65   $202.70  
  Purchase #7 $11.87   5.134%   $12.4794   $12.48   $12.50   $12.50  
  7 purchase totals = $693.72       $766.8805   $766.89   $766.90   $767.00