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	$156.48	7.563%	$168.3146	$168.31	$168.30	$168.30
Purchase #2	$132.73	11.147%	$147.5254	$147.53	$147.55	$147.50
Purchase #3	$129.98	7.424%	$139.6297	$139.63	$139.65	$139.60
Purchase #4	$235.69	6.393%	$250.7577	$250.76	$250.75	$250.80
Purchase #5	$237.27	9.671%	$260.2164	$260.22	$260.20	$260.20
Purchase #6	$72.72	8.519%	$78.915	$78.92	$78.90	$78.90
Purchase #7	$77.83	13.219%	$88.1183	$88.12	$88.10	$88.10
7 purchase totals =	$1,042.70		$1,133.4771	$1,133.49	$1,133.45	$1,133.40