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 $244.26   5.289%   $257.1789   $257.18   $257.20   $257.20  
  Purchase #2 $125.73   3.691%   $130.3707   $130.37   $130.35   $130.40  
  Purchase #3 $167.27   12.157%   $187.605   $187.61   $187.60   $187.60  
  Purchase #4 $79.91   13.701%   $90.8585   $90.86   $90.85   $90.90  
  Purchase #5 $214.99   5.782%   $227.4207   $227.42   $227.40   $227.40  
  Purchase #6 $55.98   7.831%   $60.3638   $60.36   $60.35   $60.40  
  Purchase #7 $102.81   5.814%   $108.7874   $108.79   $108.80   $108.80  
  7 purchase totals = $990.95       $1,062.5850   $1,062.59   $1,062.55   $1,062.70