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	$169.72	6.352%	$180.5006	$180.50	$180.50	$180.50
Purchase #2	$201.31	8.604%	$218.6307	$218.63	$218.65	$218.60
Purchase #3	$157.54	11.841%	$176.1943	$176.19	$176.20	$176.20
Purchase #4	$207.47	3.673%	$215.0904	$215.09	$215.10	$215.10
Purchase #5	$82.87	13.247%	$93.8478	$93.85	$93.85	$93.80
Purchase #6	$54.89	4.865%	$57.5604	$57.56	$57.55	$57.60
Purchase #7	$142.29	11.367%	$158.4641	$158.46	$158.45	$158.50
7 purchase totals =	$1,016.09		$1,100.2883	$1,100.28	$1,100.30	$1,100.30