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 $76.53   10.559%   $84.6108   $84.61   $84.60   $84.60  
  Purchase #2 $99.53   11.317%   $110.7938   $110.79   $110.80   $110.80  
  Purchase #3 $214.51   12.657%   $241.6605   $241.66   $241.65   $241.70  
  Purchase #4 $114.34   8.193%   $123.7079   $123.71   $123.70   $123.70  
  Purchase #5 $12.50   6.716%   $13.3395   $13.34   $13.35   $13.30  
  Purchase #6 $82.80   4.771%   $86.7504   $86.75   $86.75   $86.80  
  Purchase #7 $80.55   10.651%   $89.1294   $89.13   $89.15   $89.10  
  7 purchase totals = $680.76       $749.9923   $749.99   $750.00   $750.00