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 $207.28   13.512%   $235.2877   $235.29   $235.30   $235.30  
  Purchase #2 $121.37   8.452%   $131.6282   $131.63   $131.65   $131.60  
  Purchase #3 $117.88   12.346%   $132.4335   $132.43   $132.45   $132.40  
  Purchase #4 $142.87   9.546%   $156.5084   $156.51   $156.50   $156.50  
  Purchase #5 $79.83   11.273%   $88.8292   $88.83   $88.85   $88.80  
  Purchase #6 $166.89   13.423%   $189.2916   $189.29   $189.30   $189.30  
  Purchase #7 $16.89   10.382%   $18.6435   $18.64   $18.65   $18.60  
  7 purchase totals = $853.01       $952.6221   $952.62   $952.70   $952.50