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 $219.81   13.296%   $249.0359   $249.04   $249.05   $249.00  
  Purchase #2 $136.72   9.447%   $149.6359   $149.64   $149.65   $149.60  
  Purchase #3 $25.63   3.706%   $26.5798   $26.58   $26.60   $26.60  
  Purchase #4 $172.74   10.233%   $190.4165   $190.42   $190.40   $190.40  
  Purchase #5 $202.39   13.735%   $230.1883   $230.19   $230.20   $230.20  
  Purchase #6 $61.80   5.757%   $65.3578   $65.36   $65.35   $65.40  
  Purchase #7 $187.95   12.477%   $211.4005   $211.40   $211.40   $211.40  
  7 purchase totals = $1,007.04       $1,122.6147   $1,122.63   $1,122.65   $1,122.60