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	$120.79	9.532%	$132.3037	$132.30	$132.30	$132.30
Purchase #2	$53.28	4.200%	$55.5178	$55.52	$55.50	$55.50
Purchase #3	$114.64	11.119%	$127.3868	$127.39	$127.40	$127.40
Purchase #4	$165.77	8.195%	$179.3549	$179.35	$179.35	$179.40
Purchase #5	$165.78	10.719%	$183.55	$183.55	$183.55	$183.60
Purchase #6	$52.54	12.671%	$59.1973	$59.20	$59.20	$59.20
Purchase #7	$77.90	12.837%	$87.9	$87.90	$87.90	$87.90
7 purchase totals =	$750.70		$825.2105	$825.21	$825.20	$825.30