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 $195.28   12.614%   $219.9126   $219.91   $219.90   $219.90  
  Purchase #2 $243.94   5.841%   $258.1885   $258.19   $258.20   $258.20  
  Purchase #3 $105.49   11.447%   $117.5654   $117.57   $117.55   $117.60  
  Purchase #4 $241.66   4.119%   $251.614   $251.61   $251.60   $251.60  
  Purchase #5 $150.88   5.322%   $158.9098   $158.91   $158.90   $158.90  
  Purchase #6 $171.25   4.844%   $179.5454   $179.55   $179.55   $179.50  
  Purchase #7 $53.43   13.285%   $60.5282   $60.53   $60.55   $60.50  
  7 purchase totals = $1,161.93       $1,246.2639   $1,246.27   $1,246.25   $1,246.20