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	$156.54	9.810%	$171.8966	$171.90	$171.90	$171.90
Purchase #2	$143.48	9.199%	$156.6787	$156.68	$156.70	$156.70
Purchase #3	$241.75	6.702%	$257.9521	$257.95	$257.95	$258.00
Purchase #4	$78.76	13.375%	$89.2942	$89.29	$89.30	$89.30
Purchase #5	$84.91	9.422%	$92.9102	$92.91	$92.90	$92.90
Purchase #6	$86.68	3.325%	$89.5621	$89.56	$89.55	$89.60
Purchase #7	$47.29	13.102%	$53.4859	$53.49	$53.50	$53.50
7 purchase totals =	$839.41		$911.7798	$911.78	$911.80	$911.90