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 $63.68   11.852%   $71.2274   $71.23   $71.25   $71.20  
  Purchase #2 $200.34   8.798%   $217.9659   $217.97   $217.95   $218.00  
  Purchase #3 $206.32   11.732%   $230.5255   $230.53   $230.55   $230.50  
  Purchase #4 $169.91   9.468%   $185.9971   $186.00   $186.00   $186.00  
  Purchase #5 $172.76   5.413%   $182.1115   $182.11   $182.10   $182.10  
  Purchase #6 $172.76   11.280%   $192.2473   $192.25   $192.25   $192.20  
  Purchase #7 $107.42   4.770%   $112.5439   $112.54   $112.55   $112.50  
  7 purchase totals = $1,093.19       $1,192.6186   $1,192.63   $1,192.65   $1,192.50