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 $226.38   4.141%   $235.7544   $235.75   $235.75   $235.80  
  Purchase #2 $248.66   10.530%   $274.8439   $274.84   $274.85   $274.80  
  Purchase #3 $62.95   12.521%   $70.832   $70.83   $70.85   $70.80  
  Purchase #4 $83.60   11.484%   $93.2006   $93.20   $93.20   $93.20  
  Purchase #5 $127.45   10.645%   $141.0171   $141.02   $141.00   $141.00  
  Purchase #6 $118.31   7.336%   $126.9892   $126.99   $127.00   $127.00  
  Purchase #7 $77.90   4.542%   $81.4382   $81.44   $81.45   $81.40  
  7 purchase totals = $945.25       $1,024.0754   $1,024.07   $1,024.10   $1,024.00