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 $25.71   3.107%   $26.5088   $26.51   $26.50   $26.50  
  Purchase #2 $176.64   13.228%   $200.0059   $200.01   $200.00   $200.00  
  Purchase #3 $159.89   5.725%   $169.0437   $169.04   $169.05   $169.00  
  Purchase #4 $63.56   5.833%   $67.2675   $67.27   $67.25   $67.30  
  Purchase #5 $202.49   12.304%   $227.4044   $227.40   $227.40   $227.40  
  Purchase #6 $209.32   10.134%   $230.5325   $230.53   $230.55   $230.50  
  Purchase #7 $217.37   4.132%   $226.3517   $226.35   $226.35   $226.40  
  7 purchase totals = $1,054.98       $1,147.1145   $1,147.11   $1,147.10   $1,147.10