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 $68.37   12.483%   $76.9046   $76.90   $76.90   $76.90  
  Purchase #2 $92.56   11.136%   $102.8675   $102.87   $102.85   $102.90  
  Purchase #3 $171.38   13.514%   $194.5403   $194.54   $194.55   $194.50  
  Purchase #4 $163.79   5.819%   $173.3209   $173.32   $173.30   $173.30  
  Purchase #5 $196.96   10.392%   $217.4281   $217.43   $217.45   $217.40  
  Purchase #6 $192.93   9.857%   $211.9471   $211.95   $211.95   $211.90  
  Purchase #7 $166.90   9.617%   $182.9508   $182.95   $182.95   $183.00  
  7 purchase totals = $1,052.89       $1,159.9593   $1,159.96   $1,159.95   $1,159.90