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	$152.84	3.494%	$158.1802	$158.18	$158.20	$158.20
Purchase #2	$211.82	5.537%	$223.5485	$223.55	$223.55	$223.50
Purchase #3	$88.71	11.345%	$98.7741	$98.77	$98.75	$98.80
Purchase #4	$96.50	3.529%	$99.9055	$99.91	$99.90	$99.90
Purchase #5	$185.26	3.605%	$191.9386	$191.94	$191.95	$191.90
Purchase #6	$53.30	4.669%	$55.7886	$55.79	$55.80	$55.80
Purchase #7	$20.49	8.176%	$22.1653	$22.17	$22.15	$22.20
7 purchase totals =	$808.92		$850.3008	$850.31	$850.30	$850.30