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	$49.42	11.801%	$55.2521	$55.25	$55.25	$55.30
Purchase #2	$63.32	8.115%	$68.4584	$68.46	$68.45	$68.50
Purchase #3	$94.46	5.802%	$99.9406	$99.94	$99.95	$99.90
Purchase #4	$220.53	6.634%	$235.16	$235.16	$235.15	$235.20
Purchase #5	$54.61	7.463%	$58.6855	$58.69	$58.70	$58.70
Purchase #6	$111.48	11.180%	$123.9435	$123.94	$123.95	$123.90
Purchase #7	$155.45	8.348%	$168.427	$168.43	$168.45	$168.40
7 purchase totals =	$749.27		$809.8671	$809.87	$809.90	$809.90