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	$32.44	8.251%	$35.1166	$35.12	$35.10	$35.10
Purchase #2	$53.31	4.284%	$55.5938	$55.59	$55.60	$55.60
Purchase #3	$125.81	12.278%	$141.257	$141.26	$141.25	$141.30
Purchase #4	$73.41	3.548%	$76.0146	$76.01	$76.00	$76.00
Purchase #5	$84.94	6.752%	$90.6751	$90.68	$90.70	$90.70
Purchase #6	$183.76	5.104%	$193.1391	$193.14	$193.15	$193.10
Purchase #7	$80.93	11.556%	$90.2823	$90.28	$90.30	$90.30
7 purchase totals =	$634.60		$682.0785	$682.08	$682.10	$682.10