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	$167.67	11.730%	$187.3377	$187.34	$187.35	$187.30
Purchase #2	$91.33	9.454%	$99.9643	$99.96	$99.95	$100.00
Purchase #3	$131.84	4.232%	$137.4195	$137.42	$137.40	$137.40
Purchase #4	$140.68	12.815%	$158.7081	$158.71	$158.70	$158.70
Purchase #5	$238.55	3.227%	$246.248	$246.25	$246.25	$246.20
Purchase #6	$55.56	12.335%	$62.4133	$62.41	$62.40	$62.40
Purchase #7	$77.91	5.728%	$82.3727	$82.37	$82.35	$82.40
7 purchase totals =	$903.54		$974.4636	$974.46	$974.40	$974.40