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 $243.60   4.271%   $254.0042   $254.00   $254.00   $254.00  
  Purchase #2 $60.93   3.373%   $62.9852   $62.99   $63.00   $63.00  
  Purchase #3 $70.67   6.408%   $75.1985   $75.20   $75.20   $75.20  
  Purchase #4 $216.64   13.131%   $245.087   $245.09   $245.10   $245.10  
  Purchase #5 $123.48   13.136%   $139.7003   $139.70   $139.70   $139.70  
  Purchase #6 $82.69   11.332%   $92.0604   $92.06   $92.05   $92.10  
  Purchase #7 $141.65   9.439%   $155.0203   $155.02   $155.00   $155.00  
  7 purchase totals = $939.66       $1,024.0559   $1,024.06   $1,024.05   $1,024.10