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 $214.69   10.381%   $236.977   $236.98   $237.00   $237.00  
  Purchase #2 $96.80   13.497%   $109.8651   $109.87   $109.85   $109.90  
  Purchase #3 $222.25   12.604%   $250.2624   $250.26   $250.25   $250.30  
  Purchase #4 $126.33   3.354%   $130.5671   $130.57   $130.55   $130.60  
  Purchase #5 $222.82   12.406%   $250.463   $250.46   $250.45   $250.50  
  Purchase #6 $38.99   11.706%   $43.5542   $43.55   $43.55   $43.60  
  Purchase #7 $192.73   7.311%   $206.8205   $206.82   $206.80   $206.80  
  7 purchase totals = $1,114.61       $1,228.5093   $1,228.51   $1,228.45   $1,228.70