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	$90.32	10.290%	$99.6139	$99.61	$99.60	$99.60
Purchase #2	$194.73	13.112%	$220.263	$220.26	$220.25	$220.30
Purchase #3	$97.98	7.869%	$105.69	$105.69	$105.70	$105.70
Purchase #4	$57.98	5.438%	$61.133	$61.13	$61.15	$61.10
Purchase #5	$50.44	10.397%	$55.6842	$55.68	$55.70	$55.70
Purchase #6	$180.79	13.298%	$204.8315	$204.83	$204.85	$204.80
Purchase #7	$128.34	7.179%	$137.5535	$137.55	$137.55	$137.60
7 purchase totals =	$800.58		$884.7691	$884.75	$884.80	$884.80