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 $93.53   3.601%   $96.898   $96.90   $96.90   $96.90  
  Purchase #2 $14.73   12.204%   $16.5276   $16.53   $16.55   $16.50  
  Purchase #3 $223.25   4.443%   $233.169   $233.17   $233.15   $233.20  
  Purchase #4 $63.56   4.864%   $66.6516   $66.65   $66.65   $66.70  
  Purchase #5 $173.58   7.247%   $186.1593   $186.16   $186.15   $186.20  
  Purchase #6 $224.27   11.284%   $249.5766   $249.58   $249.60   $249.60  
  Purchase #7 $241.66   13.734%   $274.8496   $274.85   $274.85   $274.80  
  7 purchase totals = $1,034.58       $1,123.8317   $1,123.84   $1,123.85   $1,123.90