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	$111.77	12.335%	$125.5568	$125.56	$125.55	$125.60
Purchase #2	$64.59	8.874%	$70.3217	$70.32	$70.30	$70.30
Purchase #3	$209.43	12.559%	$235.7323	$235.73	$235.75	$235.70
Purchase #4	$10.34	9.664%	$11.3393	$11.34	$11.35	$11.30
Purchase #5	$183.29	3.821%	$190.2935	$190.29	$190.30	$190.30
Purchase #6	$101.77	3.256%	$105.0836	$105.08	$105.10	$105.10
Purchase #7	$80.48	12.551%	$90.581	$90.58	$90.60	$90.60
7 purchase totals =	$761.67		$828.9082	$828.90	$828.95	$828.90