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 $181.47   7.660%   $195.3706   $195.37   $195.35   $195.40  
  Purchase #2 $159.86   4.198%   $166.5709   $166.57   $166.55   $166.60  
  Purchase #3 $117.97   3.782%   $122.4316   $122.43   $122.45   $122.40  
  Purchase #4 $240.63   8.804%   $261.8151   $261.82   $261.80   $261.80  
  Purchase #5 $127.89   5.163%   $134.493   $134.49   $134.50   $134.50  
  Purchase #6 $124.59   13.840%   $141.8333   $141.83   $141.85   $141.80  
  Purchase #7 $235.42   11.860%   $263.3408   $263.34   $263.35   $263.30  
  7 purchase totals = $1,187.83       $1,285.8553   $1,285.85   $1,285.85   $1,285.80