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	$132.28	6.667%	$141.0991	$141.10	$141.10	$141.10
Purchase #2	$100.49	13.845%	$114.4028	$114.40	$114.40	$114.40
Purchase #3	$217.89	10.457%	$240.6748	$240.67	$240.65	$240.70
Purchase #4	$86.49	7.391%	$92.8825	$92.88	$92.90	$92.90
Purchase #5	$170.53	7.120%	$182.6717	$182.67	$182.65	$182.70
Purchase #6	$87.60	13.591%	$99.5057	$99.51	$99.50	$99.50
Purchase #7	$222.54	11.137%	$247.3243	$247.32	$247.30	$247.30
7 purchase totals =	$1,017.82		$1,118.5609	$1,118.55	$1,118.50	$1,118.60