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 $41.32   5.486%   $43.5868   $43.59   $43.60   $43.60  
  Purchase #2 $157.73   3.598%   $163.4051   $163.41   $163.40   $163.40  
  Purchase #3 $217.52   9.289%   $237.7254   $237.73   $237.75   $237.70  
  Purchase #4 $200.45   7.274%   $215.0307   $215.03   $215.05   $215.00  
  Purchase #5 $5.33   13.559%   $6.0527   $6.05   $6.05   $6.10  
  Purchase #6 $124.89   8.117%   $135.0273   $135.03   $135.05   $135.00  
  Purchase #7 $26.69   5.376%   $28.1249   $28.12   $28.10   $28.10  
  7 purchase totals = $773.93       $828.9529   $828.96   $829.00   $828.90