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 $204.82   10.860%   $227.0635   $227.06   $227.05   $227.10  
  Purchase #2 $67.41   6.838%   $72.0195   $72.02   $72.00   $72.00  
  Purchase #3 $246.65   9.423%   $269.8918   $269.89   $269.90   $269.90  
  Purchase #4 $82.98   10.628%   $91.7991   $91.80   $91.80   $91.80  
  Purchase #5 $77.68   10.483%   $85.8232   $85.82   $85.80   $85.80  
  Purchase #6 $82.90   3.710%   $85.9756   $85.98   $86.00   $86.00  
  Purchase #7 $119.93   4.842%   $125.737   $125.74   $125.75   $125.70  
  7 purchase totals = $882.37       $958.3097   $958.31   $958.30   $958.30