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	$12.26	11.518%	$13.6721	$13.67	$13.65	$13.70
Purchase #2	$129.33	8.514%	$140.3412	$140.34	$140.35	$140.30
Purchase #3	$215.71	11.839%	$241.2479	$241.25	$241.25	$241.20
Purchase #4	$119.29	7.235%	$127.9206	$127.92	$127.90	$127.90
Purchase #5	$171.43	3.600%	$177.6015	$177.60	$177.60	$177.60
Purchase #6	$210.79	6.164%	$223.7831	$223.78	$223.80	$223.80
Purchase #7	$172.52	7.689%	$185.7851	$185.79	$185.80	$185.80
7 purchase totals =	$1,031.33		$1,110.3515	$1,110.35	$1,110.35	$1,110.30