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 $58.53   4.114%   $60.9379   $60.94   $60.95   $60.90  
  Purchase #2 $244.71   10.366%   $270.0766   $270.08   $270.10   $270.10  
  Purchase #3 $173.75   8.497%   $188.5135   $188.51   $188.50   $188.50  
  Purchase #4 $35.85   12.548%   $40.3485   $40.35   $40.35   $40.30  
  Purchase #5 $91.27   5.348%   $96.1511   $96.15   $96.15   $96.20  
  Purchase #6 $137.37   9.137%   $149.9215   $149.92   $149.90   $149.90  
  Purchase #7 $241.61   3.825%   $250.8516   $250.85   $250.85   $250.90  
  7 purchase totals = $983.09       $1,056.8007   $1,056.80   $1,056.80   $1,056.80