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	$83.68	8.238%	$90.5736	$90.57	$90.55	$90.60
Purchase #2	$241.75	3.259%	$249.6286	$249.63	$249.65	$249.60
Purchase #3	$211.25	8.505%	$229.2168	$229.22	$229.20	$229.20
Purchase #4	$127.59	10.839%	$141.4195	$141.42	$141.40	$141.40
Purchase #5	$127.89	10.125%	$140.8389	$140.84	$140.85	$140.80
Purchase #6	$238.95	12.801%	$269.538	$269.54	$269.55	$269.50
Purchase #7	$227.75	6.497%	$242.5469	$242.55	$242.55	$242.50
7 purchase totals =	$1,258.86		$1,363.7623	$1,363.77	$1,363.75	$1,363.60