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	$241.60	13.160%	$273.3946	$273.39	$273.40	$273.40
Purchase #2	$173.82	6.437%	$185.0088	$185.01	$185.00	$185.00
Purchase #3	$113.57	13.339%	$128.7191	$128.72	$128.70	$128.70
Purchase #4	$34.88	13.504%	$39.5902	$39.59	$39.60	$39.60
Purchase #5	$183.95	3.867%	$191.0633	$191.06	$191.05	$191.10
Purchase #6	$65.99	4.673%	$69.0737	$69.07	$69.05	$69.10
Purchase #7	$110.78	4.322%	$115.5679	$115.57	$115.55	$115.60
7 purchase totals =	$924.59		$1,002.4176	$1,002.41	$1,002.35	$1,002.50