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	$80.28	8.248%	$86.9015	$86.90	$86.90	$86.90
Purchase #2	$152.70	4.422%	$159.4524	$159.45	$159.45	$159.50
Purchase #3	$125.49	3.123%	$129.4091	$129.41	$129.40	$129.40
Purchase #4	$131.72	4.625%	$137.8121	$137.81	$137.80	$137.80
Purchase #5	$194.29	10.691%	$215.0615	$215.06	$215.05	$215.10
Purchase #6	$72.74	7.762%	$78.3861	$78.39	$78.40	$78.40
Purchase #7	$249.45	10.567%	$275.8094	$275.81	$275.80	$275.80
7 purchase totals =	$1,006.67		$1,082.8321	$1,082.83	$1,082.80	$1,082.90