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	$6.56	11.572%	$7.3191	$7.32	$7.30	$7.30
Purchase #2	$179.94	3.296%	$185.8708	$185.87	$185.85	$185.90
Purchase #3	$65.38	3.222%	$67.4865	$67.49	$67.50	$67.50
Purchase #4	$207.46	3.272%	$214.2481	$214.25	$214.25	$214.20
Purchase #5	$57.70	7.353%	$61.9427	$61.94	$61.95	$61.90
Purchase #6	$145.36	7.495%	$156.2547	$156.25	$156.25	$156.30
Purchase #7	$46.62	4.392%	$48.6676	$48.67	$48.65	$48.70
7 purchase totals =	$709.02		$741.7895	$741.79	$741.75	$741.80