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 $242.54   11.651%   $270.7983   $270.80   $270.80   $270.80  
  Purchase #2 $66.60   13.511%   $75.5983   $75.60   $75.60   $75.60  
  Purchase #3 $48.26   10.325%   $53.2428   $53.24   $53.25   $53.20  
  Purchase #4 $167.83   4.335%   $175.1054   $175.11   $175.10   $175.10  
  Purchase #5 $240.30   4.147%   $250.2652   $250.27   $250.25   $250.30  
  Purchase #6 $108.96   6.165%   $115.6774   $115.68   $115.70   $115.70  
  Purchase #7 $164.39   7.858%   $177.3078   $177.31   $177.30   $177.30  
  7 purchase totals = $1,038.88       $1,117.9952   $1,118.01   $1,118.00   $1,118.00