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 $60.63   7.160%   $64.9711   $64.97   $64.95   $65.00  
  Purchase #2 $149.39   10.815%   $165.5465   $165.55   $165.55   $165.50  
  Purchase #3 $184.30   11.745%   $205.946   $205.95   $205.95   $205.90  
  Purchase #4 $229.35   4.337%   $239.2969   $239.30   $239.30   $239.30  
  Purchase #5 $33.68   3.627%   $34.9016   $34.90   $34.90   $34.90  
  Purchase #6 $240.28   3.186%   $247.9353   $247.94   $247.95   $247.90  
  Purchase #7 $241.68   6.321%   $256.9566   $256.96   $256.95   $257.00  
  7 purchase totals = $1,139.31       $1,215.5540   $1,215.57   $1,215.55   $1,215.50