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	$16.29	4.658%	$17.0488	$17.05	$17.05	$17.00
Purchase #2	$151.71	10.677%	$167.9081	$167.91	$167.90	$167.90
Purchase #3	$152.60	12.214%	$171.2386	$171.24	$171.25	$171.20
Purchase #4	$111.64	4.389%	$116.5399	$116.54	$116.55	$116.50
Purchase #5	$124.28	13.489%	$141.0441	$141.04	$141.05	$141.00
Purchase #6	$137.81	10.582%	$152.3931	$152.39	$152.40	$152.40
Purchase #7	$226.32	11.264%	$251.8127	$251.81	$251.80	$251.80
7 purchase totals =	$920.65		$1,017.9853	$1,017.98	$1,018.00	$1,017.80