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 $176.68   12.650%   $199.03   $199.03   $199.05   $199.00  
  Purchase #2 $130.77   3.370%   $135.1769   $135.18   $135.20   $135.20  
  Purchase #3 $205.43   10.674%   $227.3576   $227.36   $227.35   $227.40  
  Purchase #4 $250.36   3.212%   $258.4016   $258.40   $258.40   $258.40  
  Purchase #5 $51.62   11.281%   $57.4433   $57.44   $57.45   $57.40  
  Purchase #6 $219.58   8.253%   $237.7019   $237.70   $237.70   $237.70  
  Purchase #7 $99.42   12.272%   $111.6208   $111.62   $111.60   $111.60  
  7 purchase totals = $1,133.86       $1,226.7321   $1,226.73   $1,226.75   $1,226.70