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 $206.66   8.425%   $224.0711   $224.07   $224.05   $224.10  
  Purchase #2 $163.52   11.489%   $182.3068   $182.31   $182.30   $182.30  
  Purchase #3 $75.66   10.420%   $83.5438   $83.54   $83.55   $83.50  
  Purchase #4 $68.57   7.405%   $73.6476   $73.65   $73.65   $73.60  
  Purchase #5 $154.88   8.245%   $167.6499   $167.65   $167.65   $167.60  
  Purchase #6 $248.34   12.834%   $280.212   $280.21   $280.20   $280.20  
  Purchase #7 $45.86   5.134%   $48.2145   $48.21   $48.20   $48.20  
  7 purchase totals = $963.49       $1,059.6457   $1,059.64   $1,059.60   $1,059.50