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 $99.28   8.200%   $107.421   $107.42   $107.40   $107.40  
  Purchase #2 $122.63   7.770%   $132.1584   $132.16   $132.15   $132.20  
  Purchase #3 $189.60   3.864%   $196.9261   $196.93   $196.95   $196.90  
  Purchase #4 $239.51   13.152%   $271.0104   $271.01   $271.00   $271.00  
  Purchase #5 $115.47   11.717%   $128.9996   $129.00   $129.00   $129.00  
  Purchase #6 $88.56   9.800%   $97.2389   $97.24   $97.25   $97.20  
  Purchase #7 $214.59   12.228%   $240.8301   $240.83   $240.85   $240.80  
  7 purchase totals = $1,069.64       $1,174.5845   $1,174.59   $1,174.60   $1,174.50