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	$24.69	10.602%	$27.3076	$27.31	$27.30	$27.30
Purchase #2	$57.65	12.288%	$64.734	$64.73	$64.75	$64.70
Purchase #3	$218.92	13.414%	$248.2859	$248.29	$248.30	$248.30
Purchase #4	$108.51	9.231%	$118.5266	$118.53	$118.55	$118.50
Purchase #5	$72.37	6.848%	$77.3259	$77.33	$77.35	$77.30
Purchase #6	$67.61	12.212%	$75.8665	$75.87	$75.85	$75.90
Purchase #7	$52.83	5.703%	$55.8429	$55.84	$55.85	$55.80
7 purchase totals =	$602.58		$667.8894	$667.90	$667.95	$667.80