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	$136.94	5.222%	$144.091	$144.09	$144.10	$144.10
Purchase #2	$31.61	6.162%	$33.5578	$33.56	$33.55	$33.60
Purchase #3	$224.63	11.390%	$250.2154	$250.22	$250.20	$250.20
Purchase #4	$48.53	13.149%	$54.9112	$54.91	$54.90	$54.90
Purchase #5	$89.88	13.181%	$101.7271	$101.73	$101.75	$101.70
Purchase #6	$76.27	5.488%	$80.4557	$80.46	$80.45	$80.50
Purchase #7	$171.55	8.607%	$186.3153	$186.32	$186.30	$186.30
7 purchase totals =	$779.41		$851.2735	$851.29	$851.25	$851.30