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	$154.89	6.414%	$164.8246	$164.82	$164.80	$164.80
Purchase #2	$204.77	4.468%	$213.9191	$213.92	$213.90	$213.90
Purchase #3	$73.97	6.305%	$78.6338	$78.63	$78.65	$78.60
Purchase #4	$250.27	11.722%	$279.6066	$279.61	$279.60	$279.60
Purchase #5	$22.86	8.530%	$24.81	$24.81	$24.80	$24.80
Purchase #6	$105.31	13.215%	$119.2267	$119.23	$119.25	$119.20
Purchase #7	$99.25	11.397%	$110.5615	$110.56	$110.55	$110.60
7 purchase totals =	$911.32		$991.5823	$991.58	$991.55	$991.50