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	$92.98	13.489%	$105.5221	$105.52	$105.50	$105.50
Purchase #2	$41.31	9.119%	$45.0771	$45.08	$45.10	$45.10
Purchase #3	$146.67	7.401%	$157.525	$157.53	$157.55	$157.50
Purchase #4	$248.37	12.825%	$280.2235	$280.22	$280.20	$280.20
Purchase #5	$147.50	11.300%	$164.1675	$164.17	$164.15	$164.20
Purchase #6	$132.35	6.861%	$141.4305	$141.43	$141.45	$141.40
Purchase #7	$23.83	9.655%	$26.1308	$26.13	$26.15	$26.10
7 purchase totals =	$833.01		$920.0765	$920.08	$920.10	$920.00