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 $182.62   8.759%   $198.6157   $198.62   $198.60   $198.60  
  Purchase #2 $96.55   4.509%   $100.9034   $100.90   $100.90   $100.90  
  Purchase #3 $14.80   7.658%   $15.9334   $15.93   $15.95   $15.90  
  Purchase #4 $70.67   3.290%   $72.995   $73.00   $73.00   $73.00  
  Purchase #5 $26.97   9.496%   $29.5311   $29.53   $29.55   $29.50  
  Purchase #6 $247.61   11.558%   $276.2288   $276.23   $276.25   $276.20  
  Purchase #7 $89.96   9.557%   $98.5575   $98.56   $98.55   $98.60  
  7 purchase totals = $729.18       $792.7649   $792.77   $792.80   $792.70