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 $221.92   5.423%   $233.9547   $233.95   $233.95   $234.00  
  Purchase #2 $117.97   6.761%   $125.946   $125.95   $125.95   $125.90  
  Purchase #3 $84.42   8.122%   $91.2766   $91.28   $91.30   $91.30  
  Purchase #4 $160.46   13.754%   $182.5297   $182.53   $182.55   $182.50  
  Purchase #5 $179.78   3.457%   $185.995   $186.00   $186.00   $186.00  
  Purchase #6 $76.85   8.471%   $83.36   $83.36   $83.35   $83.40  
  Purchase #7 $117.89   5.155%   $123.9672   $123.97   $123.95   $124.00  
  7 purchase totals = $959.29       $1,027.0292   $1,027.04   $1,027.05   $1,027.10