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	$151.86	12.333%	$170.5889	$170.59	$170.60	$170.60
Purchase #2	$41.45	9.870%	$45.5411	$45.54	$45.55	$45.50
Purchase #3	$239.80	12.242%	$269.1563	$269.16	$269.15	$269.20
Purchase #4	$75.25	9.570%	$82.4514	$82.45	$82.45	$82.50
Purchase #5	$79.25	11.554%	$88.4065	$88.41	$88.40	$88.40
Purchase #6	$243.42	13.103%	$275.3153	$275.32	$275.30	$275.30
Purchase #7	$62.42	4.214%	$65.0504	$65.05	$65.05	$65.10
7 purchase totals =	$893.45		$996.5099	$996.52	$996.50	$996.60