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 $204.62   8.628%   $222.2746   $222.27   $222.25   $222.30  
  Purchase #2 $16.92   8.723%   $18.3959   $18.40   $18.40   $18.40  
  Purchase #3 $136.35   3.864%   $141.6186   $141.62   $141.60   $141.60  
  Purchase #4 $217.86   12.676%   $245.4759   $245.48   $245.50   $245.50  
  Purchase #5 $159.57   8.201%   $172.6563   $172.66   $172.65   $172.70  
  Purchase #6 $8.34   7.431%   $8.9597   $8.96   $8.95   $9.00  
  Purchase #7 $246.57   4.865%   $258.5656   $258.57   $258.55   $258.60  
  7 purchase totals = $990.23       $1,067.9466   $1,067.96   $1,067.90   $1,068.10