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 $66.86   6.466%   $71.1832   $71.18   $71.20   $71.20  
  Purchase #2 $78.28   5.214%   $82.3615   $82.36   $82.35   $82.40  
  Purchase #3 $155.37   6.344%   $165.2267   $165.23   $165.25   $165.20  
  Purchase #4 $82.59   5.559%   $87.1812   $87.18   $87.20   $87.20  
  Purchase #5 $11.78   10.195%   $12.981   $12.98   $13.00   $13.00  
  Purchase #6 $158.87   6.798%   $169.67   $169.67   $169.65   $169.70  
  Purchase #7 $115.95   7.243%   $124.3483   $124.35   $124.35   $124.30  
  7 purchase totals = $669.70       $712.9519   $712.95   $713.00   $713.00