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 $161.96   9.748%   $177.7479   $177.75   $177.75   $177.70  
  Purchase #2 $119.83   4.266%   $124.9419   $124.94   $124.95   $124.90  
  Purchase #3 $233.36   9.326%   $255.1232   $255.12   $255.10   $255.10  
  Purchase #4 $93.28   11.611%   $104.1107   $104.11   $104.10   $104.10  
  Purchase #5 $25.38   5.206%   $26.7013   $26.70   $26.70   $26.70  
  Purchase #6 $32.80   3.351%   $33.8991   $33.90   $33.90   $33.90  
  Purchase #7 $225.42   7.411%   $242.1259   $242.13   $242.15   $242.10  
  7 purchase totals = $892.03       $964.6500   $964.65   $964.65   $964.50