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 $208.92   12.237%   $234.4855   $234.49   $234.50   $234.50  
  Purchase #2 $101.61   6.163%   $107.8722   $107.87   $107.85   $107.90  
  Purchase #3 $47.69   9.426%   $52.1853   $52.19   $52.20   $52.20  
  Purchase #4 $34.75   13.868%   $39.5691   $39.57   $39.55   $39.60  
  Purchase #5 $224.79   10.166%   $247.6422   $247.64   $247.65   $247.60  
  Purchase #6 $203.62   3.265%   $210.2682   $210.27   $210.25   $210.30  
  Purchase #7 $11.56   5.526%   $12.1988   $12.20   $12.20   $12.20  
  7 purchase totals = $832.94       $904.2213   $904.23   $904.20   $904.30