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	$71.45	3.417%	$73.8914	$73.89	$73.90	$73.90
Purchase #2	$41.69	3.227%	$43.0353	$43.04	$43.05	$43.00
Purchase #3	$155.65	11.493%	$173.5389	$173.54	$173.55	$173.50
Purchase #4	$88.94	4.327%	$92.7884	$92.79	$92.80	$92.80
Purchase #5	$228.29	12.210%	$256.1642	$256.16	$256.15	$256.20
Purchase #6	$76.36	6.618%	$81.4135	$81.41	$81.40	$81.40
Purchase #7	$127.69	9.662%	$140.0274	$140.03	$140.05	$140.00
7 purchase totals =	$790.07		$860.8591	$860.86	$860.90	$860.80