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	$19.45	9.626%	$21.3223	$21.32	$21.30	$21.30
Purchase #2	$83.25	3.765%	$86.3844	$86.38	$86.40	$86.40
Purchase #3	$75.30	3.187%	$77.6998	$77.70	$77.70	$77.70
Purchase #4	$113.85	7.511%	$122.4013	$122.40	$122.40	$122.40
Purchase #5	$30.52	4.505%	$31.8949	$31.89	$31.90	$31.90
Purchase #6	$172.65	11.457%	$192.4305	$192.43	$192.45	$192.40
Purchase #7	$78.79	13.321%	$89.2856	$89.29	$89.30	$89.30
7 purchase totals =	$573.81		$621.4188	$621.41	$621.45	$621.40