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 $195.98   6.606%   $208.9264   $208.93   $208.95   $208.90  
  Purchase #2 $233.73   5.859%   $247.4242   $247.42   $247.40   $247.40  
  Purchase #3 $76.54   3.524%   $79.2373   $79.24   $79.25   $79.20  
  Purchase #4 $150.29   10.304%   $165.7759   $165.78   $165.80   $165.80  
  Purchase #5 $89.29   12.465%   $100.42   $100.42   $100.40   $100.40  
  Purchase #6 $216.95   13.866%   $247.0323   $247.03   $247.05   $247.00  
  Purchase #7 $200.95   9.561%   $220.1628   $220.16   $220.15   $220.20  
  7 purchase totals = $1,163.73       $1,268.9789   $1,268.98   $1,269.00   $1,268.90