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	$83.98	4.313%	$87.6021	$87.60	$87.60	$87.60
Purchase #2	$204.46	11.826%	$228.6394	$228.64	$228.65	$228.60
Purchase #3	$14.58	4.733%	$15.2701	$15.27	$15.25	$15.30
Purchase #4	$82.56	3.591%	$85.5247	$85.52	$85.50	$85.50
Purchase #5	$232.87	11.437%	$259.5033	$259.50	$259.50	$259.50
Purchase #6	$60.73	6.516%	$64.6872	$64.69	$64.70	$64.70
Purchase #7	$59.89	3.304%	$61.8688	$61.87	$61.85	$61.90
7 purchase totals =	$739.07		$803.0956	$803.09	$803.05	$803.10