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	$40.45	4.432%	$42.2427	$42.24	$42.25	$42.20
Purchase #2	$171.62	8.353%	$185.9554	$185.96	$185.95	$186.00
Purchase #3	$159.52	6.770%	$170.3195	$170.32	$170.30	$170.30
Purchase #4	$223.95	13.645%	$254.508	$254.51	$254.50	$254.50
Purchase #5	$39.55	6.864%	$42.2647	$42.26	$42.25	$42.30
Purchase #6	$138.68	6.212%	$147.2948	$147.29	$147.30	$147.30
Purchase #7	$133.57	12.311%	$150.0138	$150.01	$150.00	$150.00
7 purchase totals =	$907.34		$992.5989	$992.59	$992.55	$992.60