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	$73.39	12.291%	$82.4104	$82.41	$82.40	$82.40
Purchase #2	$37.90	7.489%	$40.7383	$40.74	$40.75	$40.70
Purchase #3	$74.72	5.665%	$78.9529	$78.95	$78.95	$79.00
Purchase #4	$190.85	9.152%	$208.3166	$208.32	$208.30	$208.30
Purchase #5	$233.61	8.534%	$253.5463	$253.55	$253.55	$253.50
Purchase #6	$54.38	8.138%	$58.8054	$58.81	$58.80	$58.80
Purchase #7	$111.80	4.703%	$117.058	$117.06	$117.05	$117.10
7 purchase totals =	$776.65		$839.8279	$839.84	$839.80	$839.80