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	$112.25	4.716%	$117.5437	$117.54	$117.55	$117.50
Purchase #2	$88.41	11.140%	$98.2589	$98.26	$98.25	$98.30
Purchase #3	$233.59	11.120%	$259.5652	$259.57	$259.55	$259.60
Purchase #4	$219.95	8.731%	$239.1538	$239.15	$239.15	$239.20
Purchase #5	$128.74	11.352%	$143.3546	$143.35	$143.35	$143.40
Purchase #6	$99.42	8.215%	$107.5874	$107.59	$107.60	$107.60
Purchase #7	$34.34	10.350%	$37.8942	$37.89	$37.90	$37.90
7 purchase totals =	$916.70		$1,003.3578	$1,003.35	$1,003.35	$1,003.50