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	$72.66	7.461%	$78.0812	$78.08	$78.10	$78.10
Purchase #2	$97.78	13.136%	$110.6244	$110.62	$110.60	$110.60
Purchase #3	$178.51	11.512%	$199.0601	$199.06	$199.05	$199.10
Purchase #4	$77.99	6.772%	$83.2715	$83.27	$83.25	$83.30
Purchase #5	$176.79	12.728%	$199.2918	$199.29	$199.30	$199.30
Purchase #6	$62.86	10.653%	$69.5565	$69.56	$69.55	$69.60
Purchase #7	$52.97	11.645%	$59.1384	$59.14	$59.15	$59.10
7 purchase totals =	$719.56		$799.0239	$799.02	$799.00	$799.10