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 $226.93   4.243%   $236.5586   $236.56   $236.55   $236.60  
  Purchase #2 $174.69   5.339%   $184.0167   $184.02   $184.00   $184.00  
  Purchase #3 $213.31   4.857%   $223.6705   $223.67   $223.65   $223.70  
  Purchase #4 $170.79   12.314%   $191.8211   $191.82   $191.80   $191.80  
  Purchase #5 $214.67   13.809%   $244.3138   $244.31   $244.30   $244.30  
  Purchase #6 $88.42   9.110%   $96.4751   $96.48   $96.50   $96.50  
  Purchase #7 $238.61   9.671%   $261.686   $261.69   $261.70   $261.70  
  7 purchase totals = $1,327.42       $1,438.5418   $1,438.55   $1,438.50   $1,438.60