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	$140.80	12.779%	$158.7928	$158.79	$158.80	$158.80
Purchase #2	$48.84	11.659%	$54.5343	$54.53	$54.55	$54.50
Purchase #3	$196.69	10.289%	$216.9274	$216.93	$216.95	$216.90
Purchase #4	$91.88	8.407%	$99.6044	$99.60	$99.60	$99.60
Purchase #5	$244.56	7.312%	$262.4422	$262.44	$262.45	$262.40
Purchase #6	$77.98	4.434%	$81.4376	$81.44	$81.45	$81.40
Purchase #7	$118.90	9.319%	$129.9803	$129.98	$130.00	$130.00
7 purchase totals =	$919.65		$1,003.7190	$1,003.71	$1,003.80	$1,003.60