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	$26.41	9.268%	$28.8577	$28.86	$28.85	$28.90
Purchase #2	$116.92	8.719%	$127.1143	$127.11	$127.10	$127.10
Purchase #3	$6.93	13.846%	$7.8895	$7.89	$7.90	$7.90
Purchase #4	$35.35	5.647%	$37.3462	$37.35	$37.35	$37.30
Purchase #5	$73.75	8.786%	$80.2297	$80.23	$80.25	$80.20
Purchase #6	$225.30	12.579%	$253.6405	$253.64	$253.65	$253.60
Purchase #7	$79.35	7.210%	$85.0711	$85.07	$85.05	$85.10
7 purchase totals =	$564.01		$620.1490	$620.15	$620.15	$620.10