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 $29.36   7.366%   $31.5227   $31.52   $31.50   $31.50  
  Purchase #2 $161.72   3.200%   $166.895   $166.90   $166.90   $166.90  
  Purchase #3 $195.90   7.332%   $210.2634   $210.26   $210.25   $210.30  
  Purchase #4 $37.71   4.703%   $39.4835   $39.48   $39.50   $39.50  
  Purchase #5 $143.47   5.835%   $151.8415   $151.84   $151.85   $151.80  
  Purchase #6 $10.46   4.734%   $10.9552   $10.96   $10.95   $11.00  
  Purchase #7 $68.25   7.273%   $73.2138   $73.21   $73.20   $73.20  
  7 purchase totals = $646.87       $684.1751   $684.17   $684.15   $684.20