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	$135.31	4.404%	$141.2691	$141.27	$141.25	$141.30
Purchase #2	$161.40	3.392%	$166.8747	$166.87	$166.85	$166.90
Purchase #3	$246.45	3.225%	$254.398	$254.40	$254.40	$254.40
Purchase #4	$229.37	13.115%	$259.4519	$259.45	$259.45	$259.50
Purchase #5	$62.33	12.820%	$70.3207	$70.32	$70.30	$70.30
Purchase #6	$146.49	9.333%	$160.1619	$160.16	$160.15	$160.20
Purchase #7	$66.83	7.188%	$71.6337	$71.63	$71.65	$71.60
7 purchase totals =	$1,048.18		$1,124.1100	$1,124.10	$1,124.05	$1,124.20