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	$143.97	10.349%	$158.8695	$158.87	$158.85	$158.90
Purchase #2	$102.64	10.867%	$113.7939	$113.79	$113.80	$113.80
Purchase #3	$198.27	6.182%	$210.5271	$210.53	$210.55	$210.50
Purchase #4	$82.73	9.300%	$90.4239	$90.42	$90.40	$90.40
Purchase #5	$148.94	4.321%	$155.3757	$155.38	$155.40	$155.40
Purchase #6	$18.52	7.177%	$19.8492	$19.85	$19.85	$19.80
Purchase #7	$33.66	4.530%	$35.1848	$35.18	$35.20	$35.20
7 purchase totals =	$728.73		$784.0241	$784.02	$784.05	$784.00