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	$164.92	4.219%	$171.878	$171.88	$171.90	$171.90
Purchase #2	$217.31	9.105%	$237.0961	$237.10	$237.10	$237.10
Purchase #3	$144.73	7.200%	$155.1506	$155.15	$155.15	$155.20
Purchase #4	$73.57	9.344%	$80.4444	$80.44	$80.45	$80.40
Purchase #5	$162.27	12.850%	$183.1217	$183.12	$183.10	$183.10
Purchase #6	$37.27	6.581%	$39.7227	$39.72	$39.70	$39.70
Purchase #7	$138.52	10.103%	$152.5147	$152.51	$152.50	$152.50
7 purchase totals =	$938.59		$1,019.9282	$1,019.92	$1,019.90	$1,019.90