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 $60.70   13.755%   $69.0493   $69.05   $69.05   $69.00  
  Purchase #2 $240.62   13.533%   $273.1831   $273.18   $273.20   $273.20  
  Purchase #3 $183.46   3.616%   $190.0939   $190.09   $190.10   $190.10  
  Purchase #4 $127.77   10.635%   $141.3583   $141.36   $141.35   $141.40  
  Purchase #5 $43.64   8.780%   $47.4716   $47.47   $47.45   $47.50  
  Purchase #6 $206.78   9.166%   $225.7335   $225.73   $225.75   $225.70  
  Purchase #7 $152.87   13.105%   $172.9036   $172.90   $172.90   $172.90  
  7 purchase totals = $1,015.84       $1,119.7933   $1,119.78   $1,119.80   $1,119.80