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 $86.75   7.382%   $93.1539   $93.15   $93.15   $93.20  
  Purchase #2 $222.32   9.230%   $242.8401   $242.84   $242.85   $242.80  
  Purchase #3 $149.69   6.321%   $159.1519   $159.15   $159.15   $159.20  
  Purchase #4 $111.47   9.714%   $122.2982   $122.30   $122.30   $122.30  
  Purchase #5 $93.32   5.587%   $98.5338   $98.53   $98.55   $98.50  
  Purchase #6 $197.77   13.516%   $224.5006   $224.50   $224.50   $224.50  
  Purchase #7 $39.99   11.333%   $44.5221   $44.52   $44.50   $44.50  
  7 purchase totals = $901.31       $985.0006   $984.99   $985.00   $985.00