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	$227.92	13.694%	$259.1314	$259.13	$259.15	$259.10
Purchase #2	$141.30	8.614%	$153.4716	$153.47	$153.45	$153.50
Purchase #3	$242.95	8.845%	$264.4389	$264.44	$264.45	$264.40
Purchase #4	$162.36	12.662%	$182.918	$182.92	$182.90	$182.90
Purchase #5	$161.77	6.313%	$171.9825	$171.98	$172.00	$172.00
Purchase #6	$53.33	11.391%	$59.4048	$59.40	$59.40	$59.40
Purchase #7	$65.57	13.161%	$74.1997	$74.20	$74.20	$74.20
7 purchase totals =	$1,055.20		$1,165.5469	$1,165.54	$1,165.55	$1,165.50