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	$204.89	6.775%	$218.7713	$218.77	$218.75	$218.80
Purchase #2	$230.72	5.356%	$243.0774	$243.08	$243.10	$243.10
Purchase #3	$120.56	6.859%	$128.8292	$128.83	$128.85	$128.80
Purchase #4	$150.69	13.714%	$171.3556	$171.36	$171.35	$171.40
Purchase #5	$74.94	5.127%	$78.7822	$78.78	$78.80	$78.80
Purchase #6	$212.32	4.216%	$221.2714	$221.27	$221.25	$221.30
Purchase #7	$25.30	4.443%	$26.4241	$26.42	$26.40	$26.40
7 purchase totals =	$1,019.42		$1,088.5112	$1,088.51	$1,088.50	$1,088.60