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 $95.48   8.678%   $103.7658   $103.77   $103.75   $103.80  
  Purchase #2 $153.67   10.358%   $169.5871   $169.59   $169.60   $169.60  
  Purchase #3 $8.44   5.253%   $8.8834   $8.88   $8.90   $8.90  
  Purchase #4 $221.84   8.770%   $241.2954   $241.30   $241.30   $241.30  
  Purchase #5 $86.43   7.147%   $92.6072   $92.61   $92.60   $92.60  
  Purchase #6 $69.47   11.417%   $77.4014   $77.40   $77.40   $77.40  
  Purchase #7 $241.80   13.325%   $274.0199   $274.02   $274.00   $274.00  
  7 purchase totals = $877.13       $967.5602   $967.57   $967.55   $967.60