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	$39.91	13.577%	$45.3286	$45.33	$45.35	$45.30
Purchase #2	$42.76	6.465%	$45.5244	$45.52	$45.50	$45.50
Purchase #3	$81.42	4.416%	$85.0155	$85.02	$85.00	$85.00
Purchase #4	$39.85	12.735%	$44.9249	$44.92	$44.90	$44.90
Purchase #5	$176.40	11.521%	$196.723	$196.72	$196.70	$196.70
Purchase #6	$18.82	7.325%	$20.1986	$20.20	$20.20	$20.20
Purchase #7	$100.60	4.122%	$104.7467	$104.75	$104.75	$104.70
7 purchase totals =	$499.76		$542.4617	$542.46	$542.40	$542.30