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	$86.32	4.531%	$90.2312	$90.23	$90.25	$90.20
Purchase #2	$63.68	10.726%	$70.5103	$70.51	$70.50	$70.50
Purchase #3	$244.26	12.199%	$274.0573	$274.06	$274.05	$274.10
Purchase #4	$59.83	5.845%	$63.3271	$63.33	$63.35	$63.30
Purchase #5	$163.89	13.358%	$185.7824	$185.78	$185.80	$185.80
Purchase #6	$156.51	6.487%	$166.6628	$166.66	$166.65	$166.70
Purchase #7	$234.63	5.377%	$247.2461	$247.25	$247.25	$247.20
7 purchase totals =	$1,009.12		$1,097.8172	$1,097.82	$1,097.85	$1,097.80