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	$75.30	6.568%	$80.2457	$80.25	$80.25	$80.20
Purchase #2	$137.36	12.750%	$154.8734	$154.87	$154.85	$154.90
Purchase #3	$114.98	11.858%	$128.6143	$128.61	$128.60	$128.60
Purchase #4	$147.32	11.864%	$164.798	$164.80	$164.80	$164.80
Purchase #5	$73.46	7.813%	$79.1994	$79.20	$79.20	$79.20
Purchase #6	$139.55	8.532%	$151.4564	$151.46	$151.45	$151.50
Purchase #7	$223.48	12.142%	$250.6149	$250.61	$250.60	$250.60
7 purchase totals =	$911.45		$1,009.8021	$1,009.80	$1,009.75	$1,009.80