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	$142.43	11.587%	$158.9334	$158.93	$158.95	$158.90
Purchase #2	$40.67	3.820%	$42.2236	$42.22	$42.20	$42.20
Purchase #3	$109.77	6.722%	$117.1487	$117.15	$117.15	$117.10
Purchase #4	$67.40	10.201%	$74.2755	$74.28	$74.30	$74.30
Purchase #5	$244.29	11.753%	$273.0014	$273.00	$273.00	$273.00
Purchase #6	$77.41	11.832%	$86.5692	$86.57	$86.55	$86.60
Purchase #7	$123.83	10.543%	$136.8854	$136.89	$136.90	$136.90
7 purchase totals =	$805.80		$889.0372	$889.04	$889.05	$889.00