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	$90.69	8.638%	$98.5238	$98.52	$98.50	$98.50
Purchase #2	$238.94	6.662%	$254.8582	$254.86	$254.85	$254.90
Purchase #3	$65.53	12.333%	$73.6118	$73.61	$73.60	$73.60
Purchase #4	$179.84	10.867%	$199.3832	$199.38	$199.40	$199.40
Purchase #5	$166.51	3.147%	$171.7501	$171.75	$171.75	$171.80
Purchase #6	$134.87	12.468%	$151.6856	$151.69	$151.70	$151.70
Purchase #7	$83.73	10.470%	$92.4965	$92.50	$92.50	$92.50
7 purchase totals =	$960.11		$1,042.3092	$1,042.31	$1,042.30	$1,042.40