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 $94.34   4.658%   $98.7344   $98.73   $98.75   $98.70  
  Purchase #2 $54.70   12.776%   $61.6885   $61.69   $61.70   $61.70  
  Purchase #3 $219.97   7.664%   $236.8285   $236.83   $236.85   $236.80  
  Purchase #4 $10.44   9.531%   $11.435   $11.44   $11.45   $11.40  
  Purchase #5 $233.43   8.401%   $253.0405   $253.04   $253.05   $253.00  
  Purchase #6 $139.26   13.705%   $158.3456   $158.35   $158.35   $158.30  
  Purchase #7 $196.85   9.726%   $215.9956   $216.00   $216.00   $216.00  
  7 purchase totals = $948.99       $1,036.0681   $1,036.08   $1,036.15   $1,035.90