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	$32.55	8.119%	$35.1927	$35.19	$35.20	$35.20
Purchase #2	$73.33	7.366%	$78.7315	$78.73	$78.75	$78.70
Purchase #3	$19.38	9.260%	$21.1746	$21.17	$21.15	$21.20
Purchase #4	$242.41	7.428%	$260.4162	$260.42	$260.40	$260.40
Purchase #5	$7.56	3.467%	$7.8221	$7.82	$7.80	$7.80
Purchase #6	$207.89	8.634%	$225.8392	$225.84	$225.85	$225.80
Purchase #7	$117.25	9.104%	$127.9244	$127.92	$127.90	$127.90
7 purchase totals =	$700.37		$757.1007	$757.09	$757.05	$757.00