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	$93.39	6.570%	$99.5257	$99.53	$99.55	$99.50
Purchase #2	$107.73	13.586%	$122.3662	$122.37	$122.35	$122.40
Purchase #3	$174.69	12.499%	$196.5245	$196.52	$196.50	$196.50
Purchase #4	$58.40	11.787%	$65.2836	$65.28	$65.30	$65.30
Purchase #5	$168.28	11.292%	$187.2822	$187.28	$187.30	$187.30
Purchase #6	$209.65	10.575%	$231.8205	$231.82	$231.80	$231.80
Purchase #7	$158.82	10.412%	$175.3563	$175.36	$175.35	$175.40
7 purchase totals =	$970.96		$1,078.1590	$1,078.16	$1,078.15	$1,078.20