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	$123.25	6.620%	$131.4092	$131.41	$131.40	$131.40
Purchase #2	$33.62	10.861%	$37.2715	$37.27	$37.25	$37.30
Purchase #3	$42.68	7.158%	$45.735	$45.74	$45.75	$45.70
Purchase #4	$180.78	10.477%	$199.7203	$199.72	$199.70	$199.70
Purchase #5	$15.92	13.129%	$18.0101	$18.01	$18.00	$18.00
Purchase #6	$24.38	13.843%	$27.7549	$27.75	$27.75	$27.80
Purchase #7	$90.31	7.634%	$97.2043	$97.20	$97.20	$97.20
7 purchase totals =	$510.94		$557.1053	$557.10	$557.05	$557.10