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	$102.30	3.317%	$105.6933	$105.69	$105.70	$105.70
Purchase #2	$83.41	10.864%	$92.4717	$92.47	$92.45	$92.50
Purchase #3	$41.53	11.383%	$46.2574	$46.26	$46.25	$46.30
Purchase #4	$165.52	13.762%	$188.2989	$188.30	$188.30	$188.30
Purchase #5	$170.59	11.842%	$190.7913	$190.79	$190.80	$190.80
Purchase #6	$110.75	6.135%	$117.5445	$117.54	$117.55	$117.50
Purchase #7	$239.75	6.626%	$255.6358	$255.64	$255.65	$255.60
7 purchase totals =	$913.85		$996.6929	$996.69	$996.70	$996.70