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	$52.78	10.110%	$58.1161	$58.12	$58.10	$58.10
Purchase #2	$203.27	8.867%	$221.294	$221.29	$221.30	$221.30
Purchase #3	$81.40	9.529%	$89.1566	$89.16	$89.15	$89.20
Purchase #4	$93.99	10.226%	$103.6014	$103.60	$103.60	$103.60
Purchase #5	$119.65	4.516%	$125.0534	$125.05	$125.05	$125.10
Purchase #6	$39.54	7.172%	$42.3758	$42.38	$42.40	$42.40
Purchase #7	$121.54	4.610%	$127.143	$127.14	$127.15	$127.10
7 purchase totals =	$712.17		$766.7403	$766.74	$766.75	$766.80