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	$238.88	8.174%	$258.4061	$258.41	$258.40	$258.40
Purchase #2	$19.85	3.377%	$20.5203	$20.52	$20.50	$20.50
Purchase #3	$21.71	3.872%	$22.5506	$22.55	$22.55	$22.60
Purchase #4	$48.56	10.232%	$53.5287	$53.53	$53.55	$53.50
Purchase #5	$63.51	13.463%	$72.0604	$72.06	$72.05	$72.10
Purchase #6	$104.53	12.479%	$117.5743	$117.57	$117.55	$117.60
Purchase #7	$106.73	6.134%	$113.2768	$113.28	$113.30	$113.30
7 purchase totals =	$603.77		$657.9172	$657.92	$657.90	$658.00