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	$51.96	10.299%	$57.3114	$57.31	$57.30	$57.30
Purchase #2	$172.46	5.714%	$182.3144	$182.31	$182.30	$182.30
Purchase #3	$159.50	7.727%	$171.8246	$171.82	$171.80	$171.80
Purchase #4	$179.39	6.205%	$190.5211	$190.52	$190.50	$190.50
Purchase #5	$57.42	12.232%	$64.4436	$64.44	$64.45	$64.40
Purchase #6	$76.55	6.675%	$81.6597	$81.66	$81.65	$81.70
Purchase #7	$32.44	4.419%	$33.8735	$33.87	$33.85	$33.90
7 purchase totals =	$729.72		$781.9483	$781.93	$781.85	$781.90