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 $60.63   9.397%   $66.3274   $66.33   $66.35   $66.30  
  Purchase #2 $206.41   12.227%   $231.6478   $231.65   $231.65   $231.60  
  Purchase #3 $83.33   4.384%   $86.9832   $86.98   $87.00   $87.00  
  Purchase #4 $25.33   11.258%   $28.1817   $28.18   $28.20   $28.20  
  Purchase #5 $164.28   3.406%   $169.8754   $169.88   $169.90   $169.90  
  Purchase #6 $30.50   7.492%   $32.7851   $32.79   $32.80   $32.80  
  Purchase #7 $85.32   4.201%   $88.9043   $88.90   $88.90   $88.90  
  7 purchase totals = $655.80       $704.7049   $704.71   $704.80   $704.70