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 $32.99   5.609%   $34.8404   $34.84   $34.85   $34.80  
  Purchase #2 $247.93   11.155%   $275.5866   $275.59   $275.60   $275.60  
  Purchase #3 $125.78   8.271%   $136.1833   $136.18   $136.20   $136.20  
  Purchase #4 $175.59   5.329%   $184.9472   $184.95   $184.95   $184.90  
  Purchase #5 $136.48   9.645%   $149.6435   $149.64   $149.65   $149.60  
  Purchase #6 $85.29   4.606%   $89.2185   $89.22   $89.20   $89.20  
  Purchase #7 $10.48   9.574%   $11.4834   $11.48   $11.50   $11.50  
  7 purchase totals = $814.54       $881.9029   $881.90   $881.95   $881.80