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 $66.32   9.148%   $72.387   $72.39   $72.40   $72.40  
  Purchase #2 $176.26   6.213%   $187.211   $187.21   $187.20   $187.20  
  Purchase #3 $187.89   13.174%   $212.6426   $212.64   $212.65   $212.60  
  Purchase #4 $60.91   5.188%   $64.07   $64.07   $64.05   $64.10  
  Purchase #5 $197.99   13.689%   $225.0929   $225.09   $225.10   $225.10  
  Purchase #6 $146.64   10.493%   $162.0269   $162.03   $162.05   $162.00  
  Purchase #7 $127.90   5.441%   $134.859   $134.86   $134.85   $134.90  
  7 purchase totals = $963.91       $1,058.2894   $1,058.29   $1,058.30   $1,058.30