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	$63.69	13.271%	$72.1423	$72.14	$72.15	$72.10
Purchase #2	$193.54	13.116%	$218.9247	$218.92	$218.90	$218.90
Purchase #3	$93.49	6.411%	$99.4836	$99.48	$99.50	$99.50
Purchase #4	$127.29	13.874%	$144.9502	$144.95	$144.95	$145.00
Purchase #5	$116.56	7.679%	$125.5106	$125.51	$125.50	$125.50
Purchase #6	$54.93	7.865%	$59.2502	$59.25	$59.25	$59.30
Purchase #7	$176.53	13.138%	$199.7225	$199.72	$199.70	$199.70
7 purchase totals =	$826.03		$919.9841	$919.97	$919.95	$920.00