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	$135.50	13.280%	$153.4944	$153.49	$153.50	$153.50
Purchase #2	$75.61	10.852%	$83.8152	$83.82	$83.80	$83.80
Purchase #3	$235.66	13.779%	$268.1316	$268.13	$268.15	$268.10
Purchase #4	$132.63	3.202%	$136.8768	$136.88	$136.90	$136.90
Purchase #5	$183.77	12.413%	$206.5814	$206.58	$206.60	$206.60
Purchase #6	$151.72	12.849%	$171.2145	$171.21	$171.20	$171.20
Purchase #7	$74.90	10.698%	$82.9128	$82.91	$82.90	$82.90
7 purchase totals =	$989.79		$1,103.0267	$1,103.02	$1,103.05	$1,103.00