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 $205.49   6.711%   $219.2804   $219.28   $219.30   $219.30  
  Purchase #2 $56.51   4.343%   $58.9642   $58.96   $58.95   $59.00  
  Purchase #3 $153.38   9.447%   $167.8698   $167.87   $167.85   $167.90  
  Purchase #4 $23.99   6.854%   $25.6343   $25.63   $25.65   $25.60  
  Purchase #5 $74.51   3.456%   $77.0851   $77.09   $77.10   $77.10  
  Purchase #6 $174.78   13.110%   $197.6937   $197.69   $197.70   $197.70  
  Purchase #7 $12.73   12.177%   $14.2801   $14.28   $14.30   $14.30  
  7 purchase totals = $701.39       $760.8076   $760.80   $760.85   $760.90