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	$38.33	10.852%	$42.4896	$42.49	$42.50	$42.50
Purchase #2	$71.77	9.691%	$78.7252	$78.73	$78.75	$78.70
Purchase #3	$29.71	12.177%	$33.3278	$33.33	$33.35	$33.30
Purchase #4	$41.52	7.706%	$44.7195	$44.72	$44.70	$44.70
Purchase #5	$99.38	7.201%	$106.5364	$106.54	$106.55	$106.50
Purchase #6	$153.41	4.267%	$159.956	$159.96	$159.95	$160.00
Purchase #7	$29.49	10.411%	$32.5602	$32.56	$32.55	$32.60
7 purchase totals =	$463.61		$498.3147	$498.33	$498.35	$498.30