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 $200.78   9.104%   $219.059   $219.06   $219.05   $219.10  
  Purchase #2 $97.36   6.683%   $103.8666   $103.87   $103.85   $103.90  
  Purchase #3 $22.87   6.625%   $24.3851   $24.39   $24.40   $24.40  
  Purchase #4 $56.96   11.796%   $63.679   $63.68   $63.70   $63.70  
  Purchase #5 $214.63   10.362%   $236.87   $236.87   $236.85   $236.90  
  Purchase #6 $122.60   11.360%   $136.5274   $136.53   $136.55   $136.50  
  Purchase #7 $35.57   8.602%   $38.6297   $38.63   $38.65   $38.60  
  7 purchase totals = $750.77       $823.0168   $823.03   $823.05   $823.10