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 $216.79   10.373%   $239.2776   $239.28   $239.30   $239.30  
  Purchase #2 $195.68   4.171%   $203.8418   $203.84   $203.85   $203.80  
  Purchase #3 $85.94   12.439%   $96.6301   $96.63   $96.65   $96.60  
  Purchase #4 $142.80   7.562%   $153.5985   $153.60   $153.60   $153.60  
  Purchase #5 $182.37   8.141%   $197.2167   $197.22   $197.20   $197.20  
  Purchase #6 $231.87   11.677%   $258.9455   $258.95   $258.95   $258.90  
  Purchase #7 $187.39   4.164%   $195.1929   $195.19   $195.20   $195.20  
  7 purchase totals = $1,242.84       $1,344.7031   $1,344.71   $1,344.75   $1,344.60