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	$23.68	5.616%	$25.0099	$25.01	$25.00	$25.00
Purchase #2	$25.45	10.286%	$28.0678	$28.07	$28.05	$28.10
Purchase #3	$38.31	11.666%	$42.7792	$42.78	$42.80	$42.80
Purchase #4	$237.84	13.562%	$270.0959	$270.10	$270.10	$270.10
Purchase #5	$118.87	9.411%	$130.0569	$130.06	$130.05	$130.10
Purchase #6	$71.83	11.822%	$80.3217	$80.32	$80.30	$80.30
Purchase #7	$147.86	3.210%	$152.6063	$152.61	$152.60	$152.60
7 purchase totals =	$663.84		$728.9377	$728.95	$728.90	$729.00