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 $68.86   11.479%   $76.7644   $76.76   $76.75   $76.80  
  Purchase #2 $152.91   8.385%   $165.7315   $165.73   $165.75   $165.70  
  Purchase #3 $48.69   10.759%   $53.9286   $53.93   $53.95   $53.90  
  Purchase #4 $229.32   4.756%   $240.2265   $240.23   $240.25   $240.20  
  Purchase #5 $102.93   12.702%   $116.0042   $116.00   $116.00   $116.00  
  Purchase #6 $157.59   12.872%   $177.875   $177.88   $177.90   $177.90  
  Purchase #7 $233.27   12.158%   $261.631   $261.63   $261.65   $261.60  
  7 purchase totals = $993.57       $1,092.1612   $1,092.16   $1,092.25   $1,092.10