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 $154.69   11.806%   $172.9527   $172.95   $172.95   $173.00  
  Purchase #2 $19.36   10.759%   $21.4429   $21.44   $21.45   $21.40  
  Purchase #3 $187.35   4.442%   $195.6721   $195.67   $195.65   $195.70  
  Purchase #4 $119.88   10.522%   $132.4938   $132.49   $132.50   $132.50  
  Purchase #5 $221.44   8.736%   $240.785   $240.79   $240.80   $240.80  
  Purchase #6 $213.46   13.234%   $241.7093   $241.71   $241.70   $241.70  
  Purchase #7 $50.69   7.648%   $54.5668   $54.57   $54.55   $54.60  
  7 purchase totals = $966.87       $1,059.6226   $1,059.62   $1,059.60   $1,059.70