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	$35.58	13.799%	$40.4897	$40.49	$40.50	$40.50
Purchase #2	$239.38	6.293%	$254.4442	$254.44	$254.45	$254.40
Purchase #3	$156.78	6.552%	$167.0522	$167.05	$167.05	$167.10
Purchase #4	$99.72	11.431%	$111.119	$111.12	$111.10	$111.10
Purchase #5	$39.44	7.416%	$42.3649	$42.36	$42.35	$42.40
Purchase #6	$79.54	7.490%	$85.4975	$85.50	$85.50	$85.50
Purchase #7	$97.41	6.514%	$103.7553	$103.76	$103.75	$103.80
7 purchase totals =	$747.85		$804.7228	$804.72	$804.70	$804.80