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	$51.55	12.113%	$57.7943	$57.79	$57.80	$57.80
Purchase #2	$224.48	4.159%	$233.8161	$233.82	$233.80	$233.80
Purchase #3	$154.42	7.834%	$166.5173	$166.52	$166.50	$166.50
Purchase #4	$171.73	4.315%	$179.1401	$179.14	$179.15	$179.10
Purchase #5	$199.32	10.135%	$219.5211	$219.52	$219.50	$219.50
Purchase #6	$181.62	9.819%	$199.4533	$199.45	$199.45	$199.50
Purchase #7	$187.56	9.644%	$205.6483	$205.65	$205.65	$205.60
7 purchase totals =	$1,170.68		$1,261.8905	$1,261.89	$1,261.85	$1,261.80