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	$78.56	8.738%	$85.4246	$85.42	$85.40	$85.40
Purchase #2	$81.82	7.193%	$87.7053	$87.71	$87.70	$87.70
Purchase #3	$231.58	10.702%	$256.3637	$256.36	$256.35	$256.40
Purchase #4	$250.45	11.753%	$279.8854	$279.89	$279.90	$279.90
Purchase #5	$111.78	5.689%	$118.1392	$118.14	$118.15	$118.10
Purchase #6	$79.87	10.469%	$88.2316	$88.23	$88.25	$88.20
Purchase #7	$176.36	11.781%	$197.137	$197.14	$197.15	$197.10
7 purchase totals =	$1,010.42		$1,112.8868	$1,112.89	$1,112.90	$1,112.80