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 $241.31   11.810%   $269.8087   $269.81   $269.80   $269.80  
  Purchase #2 $172.54   12.598%   $194.2766   $194.28   $194.30   $194.30  
  Purchase #3 $122.79   3.349%   $126.9022   $126.90   $126.90   $126.90  
  Purchase #4 $10.26   4.140%   $10.6848   $10.68   $10.70   $10.70  
  Purchase #5 $245.60   11.338%   $273.4461   $273.45   $273.45   $273.40  
  Purchase #6 $131.27   13.233%   $148.641   $148.64   $148.65   $148.60  
  Purchase #7 $23.66   8.289%   $25.6212   $25.62   $25.60   $25.60  
  7 purchase totals = $947.43       $1,049.3806   $1,049.38   $1,049.40   $1,049.30