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 $61.34   8.788%   $66.7306   $66.73   $66.75   $66.70  
  Purchase #2 $224.78   6.533%   $239.4649   $239.46   $239.45   $239.50  
  Purchase #3 $141.39   3.728%   $146.661   $146.66   $146.65   $146.70  
  Purchase #4 $43.86   3.233%   $45.278   $45.28   $45.30   $45.30  
  Purchase #5 $6.75   5.463%   $7.1188   $7.12   $7.10   $7.10  
  Purchase #6 $154.94   13.635%   $176.0661   $176.07   $176.05   $176.10  
  Purchase #7 $221.52   8.277%   $239.8552   $239.86   $239.85   $239.90  
  7 purchase totals = $854.58       $921.1746   $921.18   $921.15   $921.30