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 $206.59   6.419%   $219.851   $219.85   $219.85   $219.90  
  Purchase #2 $117.93   6.277%   $125.3325   $125.33   $125.35   $125.30  
  Purchase #3 $71.99   13.551%   $81.7454   $81.75   $81.75   $81.70  
  Purchase #4 $146.88   5.282%   $154.6382   $154.64   $154.65   $154.60  
  Purchase #5 $23.67   6.356%   $25.1745   $25.17   $25.15   $25.20  
  Purchase #6 $72.76   3.793%   $75.5198   $75.52   $75.50   $75.50  
  Purchase #7 $27.43   6.496%   $29.2119   $29.21   $29.20   $29.20  
  7 purchase totals = $667.25       $711.4733   $711.47   $711.45   $711.40