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	$75.61	4.220%	$78.8007	$78.80	$78.80	$78.80
Purchase #2	$94.70	6.484%	$100.8403	$100.84	$100.85	$100.80
Purchase #3	$214.56	4.235%	$223.6466	$223.65	$223.65	$223.60
Purchase #4	$25.92	13.133%	$29.3241	$29.32	$29.30	$29.30
Purchase #5	$35.59	9.618%	$39.013	$39.01	$39.00	$39.00
Purchase #6	$35.83	13.196%	$40.5581	$40.56	$40.55	$40.60
Purchase #7	$138.67	6.126%	$147.1649	$147.16	$147.15	$147.20
7 purchase totals =	$620.88		$659.3477	$659.34	$659.30	$659.30