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	$25.32	8.521%	$27.4775	$27.48	$27.50	$27.50
Purchase #2	$141.37	8.356%	$153.1829	$153.18	$153.20	$153.20
Purchase #3	$230.27	6.150%	$244.4316	$244.43	$244.45	$244.40
Purchase #4	$171.39	4.860%	$179.7196	$179.72	$179.70	$179.70
Purchase #5	$211.98	4.473%	$221.4619	$221.46	$221.45	$221.50
Purchase #6	$99.49	12.447%	$111.8735	$111.87	$111.85	$111.90
Purchase #7	$101.85	10.201%	$112.2397	$112.24	$112.25	$112.20
7 purchase totals =	$981.67		$1,050.3867	$1,050.38	$1,050.40	$1,050.40