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	$13.32	3.396%	$13.7723	$13.77	$13.75	$13.80
Purchase #2	$19.37	7.738%	$20.8689	$20.87	$20.85	$20.90
Purchase #3	$51.33	11.364%	$57.1631	$57.16	$57.15	$57.20
Purchase #4	$143.33	7.140%	$153.5638	$153.56	$153.55	$153.60
Purchase #5	$109.45	12.181%	$122.7821	$122.78	$122.80	$122.80
Purchase #6	$157.33	6.121%	$166.9602	$166.96	$166.95	$167.00
Purchase #7	$126.46	13.650%	$143.7218	$143.72	$143.70	$143.70
7 purchase totals =	$620.59		$678.8322	$678.82	$678.75	$679.00