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 $223.53   10.247%   $246.4351   $246.44   $246.45   $246.40  
  Purchase #2 $174.37   13.520%   $197.9448   $197.94   $197.95   $197.90  
  Purchase #3 $64.30   13.832%   $73.194   $73.19   $73.20   $73.20  
  Purchase #4 $192.54   4.778%   $201.7396   $201.74   $201.75   $201.70  
  Purchase #5 $221.80   3.603%   $229.7915   $229.79   $229.80   $229.80  
  Purchase #6 $117.62   10.566%   $130.0477   $130.05   $130.05   $130.00  
  Purchase #7 $211.36   10.729%   $234.0368   $234.04   $234.05   $234.00  
  7 purchase totals = $1,205.52       $1,313.1895   $1,313.19   $1,313.25   $1,313.00