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 $114.77   3.831%   $119.1668   $119.17   $119.15   $119.20  
  Purchase #2 $51.58   10.277%   $56.8809   $56.88   $56.90   $56.90  
  Purchase #3 $205.40   12.488%   $231.0504   $231.05   $231.05   $231.10  
  Purchase #4 $34.47   4.652%   $36.0735   $36.07   $36.05   $36.10  
  Purchase #5 $189.75   3.826%   $197.0098   $197.01   $197.00   $197.00  
  Purchase #6 $113.25   6.303%   $120.3881   $120.39   $120.40   $120.40  
  Purchase #7 $7.53   13.759%   $8.5661   $8.57   $8.55   $8.60  
  7 purchase totals = $716.75       $769.1356   $769.14   $769.10   $769.30