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	$77.87	5.388%	$82.0656	$82.07	$82.05	$82.10
Purchase #2	$166.34	12.113%	$186.4888	$186.49	$186.50	$186.50
Purchase #3	$28.72	3.867%	$29.8306	$29.83	$29.85	$29.80
Purchase #4	$156.97	3.559%	$162.5566	$162.56	$162.55	$162.60
Purchase #5	$146.57	3.340%	$151.4654	$151.47	$151.45	$151.50
Purchase #6	$39.52	3.601%	$40.9431	$40.94	$40.95	$40.90
Purchase #7	$135.93	7.472%	$146.0867	$146.09	$146.10	$146.10
7 purchase totals =	$751.92		$799.4368	$799.45	$799.45	$799.50