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 $69.51   9.759%   $76.2935   $76.29   $76.30   $76.30  
  Purchase #2 $82.95   10.734%   $91.8539   $91.85   $91.85   $91.90  
  Purchase #3 $130.29   8.116%   $140.8643   $140.86   $140.85   $140.90  
  Purchase #4 $155.50   5.436%   $163.953   $163.95   $163.95   $164.00  
  Purchase #5 $226.45   8.682%   $246.1104   $246.11   $246.10   $246.10  
  Purchase #6 $134.69   8.738%   $146.4592   $146.46   $146.45   $146.50  
  Purchase #7 $168.78   10.341%   $186.2335   $186.23   $186.25   $186.20  
  7 purchase totals = $968.17       $1,051.7678   $1,051.75   $1,051.75   $1,051.90