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	$49.41	10.336%	$54.517	$54.52	$54.50	$54.50
Purchase #2	$39.59	7.623%	$42.6079	$42.61	$42.60	$42.60
Purchase #3	$65.30	12.159%	$73.2398	$73.24	$73.25	$73.20
Purchase #4	$236.90	3.189%	$244.4547	$244.45	$244.45	$244.50
Purchase #5	$8.94	12.560%	$10.0629	$10.06	$10.05	$10.10
Purchase #6	$217.50	10.564%	$240.4767	$240.48	$240.50	$240.50
Purchase #7	$54.33	3.295%	$56.1202	$56.12	$56.10	$56.10
7 purchase totals =	$671.97		$721.4792	$721.48	$721.45	$721.50