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 $216.52   13.105%   $244.8949   $244.89   $244.90   $244.90  
  Purchase #2 $57.71   11.381%   $64.278   $64.28   $64.30   $64.30  
  Purchase #3 $195.47   7.181%   $209.5067   $209.51   $209.50   $209.50  
  Purchase #4 $241.91   4.229%   $252.1404   $252.14   $252.15   $252.10  
  Purchase #5 $163.98   10.556%   $181.2897   $181.29   $181.30   $181.30  
  Purchase #6 $165.46   8.208%   $179.041   $179.04   $179.05   $179.00  
  Purchase #7 $195.63   9.141%   $213.5125   $213.51   $213.50   $213.50  
  7 purchase totals = $1,236.68       $1,344.6632   $1,344.66   $1,344.70   $1,344.60