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	$62.67	12.205%	$70.3189	$70.32	$70.30	$70.30
Purchase #2	$130.61	7.564%	$140.4893	$140.49	$140.50	$140.50
Purchase #3	$86.27	7.467%	$92.7118	$92.71	$92.70	$92.70
Purchase #4	$101.90	10.193%	$112.2867	$112.29	$112.30	$112.30
Purchase #5	$231.75	9.521%	$253.8149	$253.81	$253.80	$253.80
Purchase #6	$39.87	13.735%	$45.3461	$45.35	$45.35	$45.30
Purchase #7	$156.38	7.523%	$168.1445	$168.14	$168.15	$168.10
7 purchase totals =	$809.45		$883.1122	$883.11	$883.10	$883.00