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 $142.86   6.675%   $152.3959   $152.40   $152.40   $152.40  
  Purchase #2 $96.37   7.764%   $103.8522   $103.85   $103.85   $103.90  
  Purchase #3 $110.32   13.195%   $124.8767   $124.88   $124.90   $124.90  
  Purchase #4 $184.82   4.599%   $193.3199   $193.32   $193.30   $193.30  
  Purchase #5 $109.54   11.291%   $121.9082   $121.91   $121.90   $121.90  
  Purchase #6 $237.81   7.622%   $255.9359   $255.94   $255.95   $255.90  
  Purchase #7 $240.27   9.868%   $263.9798   $263.98   $264.00   $264.00  
  7 purchase totals = $1,121.99       $1,216.2686   $1,216.28   $1,216.30   $1,216.30