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	$37.34	7.783%	$40.2462	$40.25	$40.25	$40.20
Purchase #2	$14.43	3.859%	$14.9869	$14.99	$15.00	$15.00
Purchase #3	$165.91	4.227%	$172.923	$172.92	$172.90	$172.90
Purchase #4	$42.94	5.484%	$45.2948	$45.29	$45.30	$45.30
Purchase #5	$105.93	11.565%	$118.1808	$118.18	$118.20	$118.20
Purchase #6	$201.38	5.469%	$212.3935	$212.39	$212.40	$212.40
Purchase #7	$56.73	4.467%	$59.2641	$59.26	$59.25	$59.30
7 purchase totals =	$624.66		$663.2893	$663.28	$663.30	$663.30