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 $66.81   6.285%   $71.009   $71.01   $71.00   $71.00  
  Purchase #2 $65.91   6.106%   $69.9345   $69.93   $69.95   $69.90  
  Purchase #3 $240.55   7.746%   $259.183   $259.18   $259.20   $259.20  
  Purchase #4 $73.50   3.554%   $76.1122   $76.11   $76.10   $76.10  
  Purchase #5 $99.25   9.320%   $108.5001   $108.50   $108.50   $108.50  
  Purchase #6 $121.90   8.442%   $132.1908   $132.19   $132.20   $132.20  
  Purchase #7 $159.25   4.120%   $165.8111   $165.81   $165.80   $165.80  
  7 purchase totals = $827.17       $882.7407   $882.73   $882.75   $882.70