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	$74.28	10.803%	$82.3045	$82.30	$82.30	$82.30
Purchase #2	$53.61	12.283%	$60.1949	$60.19	$60.20	$60.20
Purchase #3	$157.68	7.743%	$169.8892	$169.89	$169.90	$169.90
Purchase #4	$81.88	5.636%	$86.4948	$86.49	$86.50	$86.50
Purchase #5	$55.95	5.521%	$59.039	$59.04	$59.05	$59.00
Purchase #6	$39.68	9.316%	$43.3766	$43.38	$43.40	$43.40
Purchase #7	$43.40	5.857%	$45.9419	$45.94	$45.95	$45.90
7 purchase totals =	$506.48		$547.2409	$547.23	$547.30	$547.20