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	$84.54	5.634%	$89.303	$89.30	$89.30	$89.30
Purchase #2	$175.40	7.331%	$188.2586	$188.26	$188.25	$188.30
Purchase #3	$241.27	9.779%	$264.8638	$264.86	$264.85	$264.90
Purchase #4	$65.77	12.711%	$74.13	$74.13	$74.15	$74.10
Purchase #5	$179.99	6.840%	$192.3013	$192.30	$192.30	$192.30
Purchase #6	$65.81	10.418%	$72.6661	$72.67	$72.65	$72.70
Purchase #7	$77.90	7.123%	$83.4488	$83.45	$83.45	$83.40
7 purchase totals =	$890.68		$964.9716	$964.97	$964.95	$965.00