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	$221.40	13.355%	$250.968	$250.97	$250.95	$251.00
Purchase #2	$106.47	11.262%	$118.4607	$118.46	$118.45	$118.50
Purchase #3	$75.81	4.855%	$79.4906	$79.49	$79.50	$79.50
Purchase #4	$93.63	12.483%	$105.3178	$105.32	$105.30	$105.30
Purchase #5	$71.58	13.824%	$81.4752	$81.48	$81.50	$81.50
Purchase #6	$221.28	3.140%	$228.2282	$228.23	$228.25	$228.20
Purchase #7	$136.31	10.824%	$151.0642	$151.06	$151.05	$151.10
7 purchase totals =	$926.48		$1,015.0047	$1,015.01	$1,015.00	$1,015.10