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	$95.34	11.406%	$106.2145	$106.21	$106.20	$106.20
Purchase #2	$140.73	12.820%	$158.7716	$158.77	$158.75	$158.80
Purchase #3	$105.84	9.349%	$115.735	$115.74	$115.75	$115.70
Purchase #4	$97.81	11.706%	$109.2596	$109.26	$109.25	$109.30
Purchase #5	$68.89	13.734%	$78.3514	$78.35	$78.35	$78.40
Purchase #6	$50.87	4.622%	$53.2212	$53.22	$53.20	$53.20
Purchase #7	$53.70	11.446%	$59.8465	$59.85	$59.85	$59.80
7 purchase totals =	$613.18		$681.3998	$681.40	$681.35	$681.40