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 $85.73   9.279%   $93.6849   $93.68   $93.70   $93.70  
  Purchase #2 $135.63   9.576%   $148.6179   $148.62   $148.60   $148.60  
  Purchase #3 $193.92   6.508%   $206.5403   $206.54   $206.55   $206.50  
  Purchase #4 $95.71   11.268%   $106.4946   $106.49   $106.50   $106.50  
  Purchase #5 $68.51   11.797%   $76.5921   $76.59   $76.60   $76.60  
  Purchase #6 $232.28   10.780%   $257.3198   $257.32   $257.30   $257.30  
  Purchase #7 $49.42   4.239%   $51.5149   $51.51   $51.50   $51.50  
  7 purchase totals = $861.20       $940.7645   $940.75   $940.75   $940.70