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 $232.26   7.489%   $249.654   $249.65   $249.65   $249.70  
  Purchase #2 $68.95   11.145%   $76.6345   $76.63   $76.65   $76.60  
  Purchase #3 $169.81   13.819%   $193.276   $193.28   $193.30   $193.30  
  Purchase #4 $126.71   8.782%   $137.8377   $137.84   $137.85   $137.80  
  Purchase #5 $248.25   11.233%   $276.1359   $276.14   $276.15   $276.10  
  Purchase #6 $106.60   8.616%   $115.7847   $115.78   $115.80   $115.80  
  Purchase #7 $66.41   9.754%   $72.8876   $72.89   $72.90   $72.90  
  7 purchase totals = $1,018.99       $1,122.2104   $1,122.21   $1,122.30   $1,122.20