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 $41.57   7.633%   $44.743   $44.74   $44.75   $44.70  
  Purchase #2 $172.46   13.660%   $196.018   $196.02   $196.00   $196.00  
  Purchase #3 $54.65   5.726%   $57.7793   $57.78   $57.80   $57.80  
  Purchase #4 $187.97   10.511%   $207.7275   $207.73   $207.75   $207.70  
  Purchase #5 $140.85   3.763%   $146.1502   $146.15   $146.15   $146.20  
  Purchase #6 $109.61   3.704%   $113.67   $113.67   $113.65   $113.70  
  Purchase #7 $207.88   12.368%   $233.5906   $233.59   $233.60   $233.60  
  7 purchase totals = $914.99       $999.6786   $999.68   $999.70   $999.70