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 $218.36   6.535%   $232.6298   $232.63   $232.65   $232.60  
  Purchase #2 $246.70   10.423%   $272.4135   $272.41   $272.40   $272.40  
  Purchase #3 $104.83   13.820%   $119.3175   $119.32   $119.30   $119.30  
  Purchase #4 $138.25   8.167%   $149.5409   $149.54   $149.55   $149.50  
  Purchase #5 $60.68   3.513%   $62.8117   $62.81   $62.80   $62.80  
  Purchase #6 $229.74   11.827%   $256.9113   $256.91   $256.90   $256.90  
  Purchase #7 $111.76   12.489%   $125.7177   $125.72   $125.70   $125.70  
  7 purchase totals = $1,110.32       $1,219.3424   $1,219.34   $1,219.30   $1,219.20