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 $242.81   11.147%   $269.876   $269.88   $269.90   $269.90  
  Purchase #2 $88.78   10.277%   $97.9039   $97.90   $97.90   $97.90  
  Purchase #3 $211.53   6.563%   $225.4127   $225.41   $225.40   $225.40  
  Purchase #4 $13.42   7.667%   $14.4489   $14.45   $14.45   $14.40  
  Purchase #5 $98.78   4.276%   $103.0038   $103.00   $103.00   $103.00  
  Purchase #6 $95.97   13.605%   $109.0267   $109.03   $109.05   $109.00  
  Purchase #7 $93.64   4.781%   $98.1169   $98.12   $98.10   $98.10  
  7 purchase totals = $844.93       $917.7889   $917.79   $917.80   $917.70