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	$136.95	7.451%	$147.1541	$147.15	$147.15	$147.20
Purchase #2	$191.32	6.346%	$203.4612	$203.46	$203.45	$203.50
Purchase #3	$219.91	9.167%	$240.0691	$240.07	$240.05	$240.10
Purchase #4	$69.71	5.443%	$73.5043	$73.50	$73.50	$73.50
Purchase #5	$51.85	5.138%	$54.5141	$54.51	$54.50	$54.50
Purchase #6	$88.86	3.423%	$91.9017	$91.90	$91.90	$91.90
Purchase #7	$160.98	6.368%	$171.2312	$171.23	$171.25	$171.20
7 purchase totals =	$919.58		$981.8357	$981.82	$981.80	$981.90