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	$228.51	13.143%	$258.5431	$258.54	$258.55	$258.50
Purchase #2	$231.74	11.356%	$258.0564	$258.06	$258.05	$258.10
Purchase #3	$91.76	8.234%	$99.3155	$99.32	$99.30	$99.30
Purchase #4	$132.33	9.181%	$144.4792	$144.48	$144.50	$144.50
Purchase #5	$97.39	3.386%	$100.6876	$100.69	$100.70	$100.70
Purchase #6	$30.66	12.232%	$34.4103	$34.41	$34.40	$34.40
Purchase #7	$92.45	13.376%	$104.8161	$104.82	$104.80	$104.80
7 purchase totals =	$904.84		$1,000.3082	$1,000.32	$1,000.30	$1,000.30