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 $86.32   6.536%   $91.9619   $91.96   $91.95   $92.00  
  Purchase #2 $119.71   10.564%   $132.3562   $132.36   $132.35   $132.40  
  Purchase #3 $7.94   3.556%   $8.2223   $8.22   $8.20   $8.20  
  Purchase #4 $232.99   8.311%   $252.3538   $252.35   $252.35   $252.40  
  Purchase #5 $220.86   12.213%   $247.8336   $247.83   $247.85   $247.80  
  Purchase #6 $115.59   10.159%   $127.3328   $127.33   $127.35   $127.30  
  Purchase #7 $188.68   5.738%   $199.5065   $199.51   $199.50   $199.50  
  7 purchase totals = $972.09       $1,059.5671   $1,059.56   $1,059.55   $1,059.60