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	$68.82	13.293%	$77.9682	$77.97	$77.95	$78.00
Purchase #2	$105.72	13.634%	$120.1339	$120.13	$120.15	$120.10
Purchase #3	$134.55	8.708%	$146.2666	$146.27	$146.25	$146.30
Purchase #4	$79.30	12.295%	$89.0499	$89.05	$89.05	$89.00
Purchase #5	$72.25	8.631%	$78.4859	$78.49	$78.50	$78.50
Purchase #6	$175.83	9.644%	$192.787	$192.79	$192.80	$192.80
Purchase #7	$115.42	13.790%	$131.3364	$131.34	$131.35	$131.30
7 purchase totals =	$751.89		$836.0279	$836.04	$836.05	$836.00