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 $172.39   8.297%   $186.6932   $186.69   $186.70   $186.70  
  Purchase #2 $248.53   10.795%   $275.3588   $275.36   $275.35   $275.40  
  Purchase #3 $120.95   5.135%   $127.1608   $127.16   $127.15   $127.20  
  Purchase #4 $61.57   13.565%   $69.922   $69.92   $69.90   $69.90  
  Purchase #5 $5.99   7.310%   $6.4279   $6.43   $6.45   $6.40  
  Purchase #6 $110.32   7.224%   $118.2895   $118.29   $118.30   $118.30  
  Purchase #7 $98.44   10.827%   $109.0981   $109.10   $109.10   $109.10  
  7 purchase totals = $818.19       $892.9503   $892.95   $892.95   $893.00