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 $89.28   6.614%   $95.185   $95.19   $95.20   $95.20  
  Purchase #2 $177.39   12.211%   $199.0511   $199.05   $199.05   $199.10  
  Purchase #3 $12.68   6.733%   $13.5337   $13.53   $13.55   $13.50  
  Purchase #4 $167.47   8.159%   $181.1339   $181.13   $181.15   $181.10  
  Purchase #5 $44.31   10.388%   $48.9129   $48.91   $48.90   $48.90  
  Purchase #6 $231.73   11.771%   $259.0069   $259.01   $259.00   $259.00  
  Purchase #7 $194.71   8.385%   $211.0364   $211.04   $211.05   $211.00  
  7 purchase totals = $917.57       $1,007.8599   $1,007.86   $1,007.90   $1,007.80