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	$142.43	11.554%	$158.8864	$158.89	$158.90	$158.90
Purchase #2	$228.98	12.871%	$258.452	$258.45	$258.45	$258.50
Purchase #3	$160.33	11.851%	$179.3307	$179.33	$179.35	$179.30
Purchase #4	$47.29	12.519%	$53.2102	$53.21	$53.20	$53.20
Purchase #5	$54.82	13.690%	$62.3249	$62.32	$62.30	$62.30
Purchase #6	$120.42	9.414%	$131.7563	$131.76	$131.75	$131.80
Purchase #7	$17.32	6.391%	$18.4269	$18.43	$18.45	$18.40
7 purchase totals =	$771.59		$862.3874	$862.39	$862.40	$862.40