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	$5.47	6.717%	$5.8374	$5.84	$5.85	$5.80
Purchase #2	$154.83	9.390%	$169.3685	$169.37	$169.35	$169.40
Purchase #3	$191.97	6.692%	$204.8166	$204.82	$204.80	$204.80
Purchase #4	$152.59	3.845%	$158.4571	$158.46	$158.45	$158.50
Purchase #5	$90.83	4.498%	$94.9155	$94.92	$94.90	$94.90
Purchase #6	$115.64	10.726%	$128.0435	$128.04	$128.05	$128.00
Purchase #7	$182.63	7.524%	$196.3711	$196.37	$196.35	$196.40
7 purchase totals =	$893.96		$957.8097	$957.82	$957.75	$957.80