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 $245.86   9.525%   $269.2782   $269.28   $269.30   $269.30  
  Purchase #2 $193.92   13.332%   $219.7734   $219.77   $219.75   $219.80  
  Purchase #3 $24.27   12.326%   $27.2615   $27.26   $27.25   $27.30  
  Purchase #4 $232.49   10.791%   $257.578   $257.58   $257.60   $257.60  
  Purchase #5 $13.63   9.671%   $14.9482   $14.95   $14.95   $14.90  
  Purchase #6 $132.47   3.115%   $136.5964   $136.60   $136.60   $136.60  
  Purchase #7 $248.78   11.782%   $278.0913   $278.09   $278.10   $278.10  
  7 purchase totals = $1,091.42       $1,203.5270   $1,203.53   $1,203.55   $1,203.60