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	$17.78	13.116%	$20.112	$20.11	$20.10	$20.10
Purchase #2	$89.80	11.723%	$100.3273	$100.33	$100.35	$100.30
Purchase #3	$130.81	3.580%	$135.493	$135.49	$135.50	$135.50
Purchase #4	$233.81	13.263%	$264.8202	$264.82	$264.80	$264.80
Purchase #5	$128.32	12.563%	$144.4408	$144.44	$144.45	$144.40
Purchase #6	$184.52	5.292%	$194.2848	$194.28	$194.30	$194.30
Purchase #7	$124.36	5.726%	$131.4809	$131.48	$131.50	$131.50
7 purchase totals =	$909.40		$990.9590	$990.95	$991.00	$990.90