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 $209.74   8.203%   $226.945   $226.95   $226.95   $226.90  
  Purchase #2 $144.67   9.691%   $158.69   $158.69   $158.70   $158.70  
  Purchase #3 $17.68   11.187%   $19.6579   $19.66   $19.65   $19.70  
  Purchase #4 $193.71   3.542%   $200.5712   $200.57   $200.55   $200.60  
  Purchase #5 $6.27   3.421%   $6.4845   $6.48   $6.50   $6.50  
  Purchase #6 $145.55   3.782%   $151.0547   $151.05   $151.05   $151.10  
  Purchase #7 $246.41   3.777%   $255.7169   $255.72   $255.70   $255.70  
  7 purchase totals = $964.03       $1,019.1202   $1,019.12   $1,019.10   $1,019.20