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 $209.33   7.133%   $224.2615   $224.26   $224.25   $224.30  
  Purchase #2 $36.62   3.278%   $37.8204   $37.82   $37.80   $37.80  
  Purchase #3 $41.25   8.113%   $44.5966   $44.60   $44.60   $44.60  
  Purchase #4 $30.68   13.125%   $34.7068   $34.71   $34.70   $34.70  
  Purchase #5 $206.55   8.235%   $223.5594   $223.56   $223.55   $223.60  
  Purchase #6 $231.83   10.218%   $255.5184   $255.52   $255.50   $255.50  
  Purchase #7 $123.63   13.374%   $140.1643   $140.16   $140.15   $140.20  
  7 purchase totals = $879.89       $960.6274   $960.63   $960.55   $960.70