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	$155.67	12.428%	$175.0167	$175.02	$175.00	$175.00
Purchase #2	$73.76	13.732%	$83.8887	$83.89	$83.90	$83.90
Purchase #3	$59.37	11.828%	$66.3923	$66.39	$66.40	$66.40
Purchase #4	$26.47	11.526%	$29.5209	$29.52	$29.50	$29.50
Purchase #5	$49.59	11.735%	$55.4094	$55.41	$55.40	$55.40
Purchase #6	$45.77	11.705%	$51.1274	$51.13	$51.15	$51.10
Purchase #7	$133.41	9.673%	$146.3147	$146.31	$146.30	$146.30
7 purchase totals =	$544.04		$607.6701	$607.67	$607.65	$607.60