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	$31.95	9.308%	$34.9239	$34.92	$34.90	$34.90
Purchase #2	$45.33	3.780%	$47.0435	$47.04	$47.05	$47.00
Purchase #3	$189.67	13.307%	$214.9094	$214.91	$214.90	$214.90
Purchase #4	$247.45	10.258%	$272.8334	$272.83	$272.85	$272.80
Purchase #5	$118.83	12.195%	$133.3213	$133.32	$133.30	$133.30
Purchase #6	$209.83	11.311%	$233.5639	$233.56	$233.55	$233.60
Purchase #7	$169.25	10.250%	$186.5981	$186.60	$186.60	$186.60
7 purchase totals =	$1,012.31		$1,123.1935	$1,123.18	$1,123.15	$1,123.10