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	$93.86	5.131%	$98.676	$98.68	$98.70	$98.70
Purchase #2	$66.80	8.157%	$72.2489	$72.25	$72.25	$72.20
Purchase #3	$174.59	8.159%	$188.8348	$188.83	$188.85	$188.80
Purchase #4	$94.27	6.597%	$100.489	$100.49	$100.50	$100.50
Purchase #5	$45.53	10.127%	$50.1408	$50.14	$50.15	$50.10
Purchase #6	$233.83	10.173%	$257.6175	$257.62	$257.60	$257.60
Purchase #7	$124.60	11.251%	$138.6187	$138.62	$138.60	$138.60
7 purchase totals =	$833.48		$906.6257	$906.63	$906.65	$906.50