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 $60.81   11.372%   $67.7253   $67.73   $67.75   $67.70  
  Purchase #2 $203.93   6.687%   $217.5668   $217.57   $217.55   $217.60  
  Purchase #3 $101.28   4.350%   $105.6857   $105.69   $105.70   $105.70  
  Purchase #4 $172.30   12.750%   $194.2683   $194.27   $194.25   $194.30  
  Purchase #5 $67.47   10.609%   $74.6279   $74.63   $74.65   $74.60  
  Purchase #6 $183.81   13.501%   $208.6262   $208.63   $208.65   $208.60  
  Purchase #7 $228.84   11.602%   $255.39   $255.39   $255.40   $255.40  
  7 purchase totals = $1,018.44       $1,123.8902   $1,123.91   $1,123.95   $1,123.90