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	$47.31	5.650%	$49.983	$49.98	$50.00	$50.00
Purchase #2	$201.82	8.717%	$219.4126	$219.41	$219.40	$219.40
Purchase #3	$80.42	10.699%	$89.0241	$89.02	$89.00	$89.00
Purchase #4	$157.46	6.483%	$167.6681	$167.67	$167.65	$167.70
Purchase #5	$123.73	12.693%	$139.435	$139.44	$139.45	$139.40
Purchase #6	$12.81	3.656%	$13.2783	$13.28	$13.30	$13.30
Purchase #7	$195.70	13.854%	$222.8123	$222.81	$222.80	$222.80
7 purchase totals =	$819.25		$901.6134	$901.61	$901.60	$901.60