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 $245.63   5.428%   $258.9628   $258.96   $258.95   $259.00  
  Purchase #2 $125.75   13.425%   $142.6319   $142.63   $142.65   $142.60  
  Purchase #3 $64.77   11.261%   $72.0637   $72.06   $72.05   $72.10  
  Purchase #4 $230.74   12.636%   $259.8963   $259.90   $259.90   $259.90  
  Purchase #5 $175.98   11.744%   $196.6471   $196.65   $196.65   $196.60  
  Purchase #6 $215.30   8.221%   $232.9998   $233.00   $233.00   $233.00  
  Purchase #7 $66.45   3.574%   $68.8249   $68.82   $68.80   $68.80  
  7 purchase totals = $1,124.62       $1,232.0265   $1,232.02   $1,232.00   $1,232.00