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 $19.36   5.842%   $20.491   $20.49   $20.50   $20.50  
  Purchase #2 $150.25   10.579%   $166.1449   $166.14   $166.15   $166.10  
  Purchase #3 $153.49   4.276%   $160.0532   $160.05   $160.05   $160.10  
  Purchase #4 $133.44   3.374%   $137.9423   $137.94   $137.95   $137.90  
  Purchase #5 $29.62   6.184%   $31.4517   $31.45   $31.45   $31.50  
  Purchase #6 $127.52   10.857%   $141.3648   $141.36   $141.35   $141.40  
  Purchase #7 $57.71   4.207%   $60.1379   $60.14   $60.15   $60.10  
  7 purchase totals = $671.39       $717.5858   $717.57   $717.60   $717.60