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	$116.53	5.802%	$123.2911	$123.29	$123.30	$123.30
Purchase #2	$149.62	8.831%	$162.8329	$162.83	$162.85	$162.80
Purchase #3	$141.77	13.325%	$160.6609	$160.66	$160.65	$160.70
Purchase #4	$150.77	5.219%	$158.6387	$158.64	$158.65	$158.60
Purchase #5	$32.77	9.483%	$35.8776	$35.88	$35.90	$35.90
Purchase #6	$175.97	11.616%	$196.4107	$196.41	$196.40	$196.40
Purchase #7	$6.76	7.836%	$7.2897	$7.29	$7.30	$7.30
7 purchase totals =	$774.19		$845.0016	$845.00	$845.05	$845.00