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	$18.41	11.548%	$20.536	$20.54	$20.55	$20.50
Purchase #2	$53.90	10.681%	$59.6571	$59.66	$59.65	$59.70
Purchase #3	$159.27	9.394%	$174.2318	$174.23	$174.25	$174.20
Purchase #4	$57.31	4.585%	$59.9377	$59.94	$59.95	$59.90
Purchase #5	$144.43	6.311%	$153.545	$153.55	$153.55	$153.50
Purchase #6	$188.85	9.519%	$206.8266	$206.83	$206.85	$206.80
Purchase #7	$180.53	11.687%	$201.6285	$201.63	$201.65	$201.60
7 purchase totals =	$802.70		$876.3627	$876.38	$876.45	$876.20