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 $91.49   4.770%   $95.8541   $95.85   $95.85   $95.90  
  Purchase #2 $194.91   9.419%   $213.2686   $213.27   $213.25   $213.30  
  Purchase #3 $163.57   3.829%   $169.8331   $169.83   $169.85   $169.80  
  Purchase #4 $69.96   5.649%   $73.912   $73.91   $73.90   $73.90  
  Purchase #5 $70.46   3.833%   $73.1607   $73.16   $73.15   $73.20  
  Purchase #6 $22.60   4.301%   $23.572   $23.57   $23.55   $23.60  
  Purchase #7 $106.25   7.847%   $114.5874   $114.59   $114.60   $114.60  
  7 purchase totals = $719.24       $764.1879   $764.18   $764.15   $764.30