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	$149.56	12.358%	$168.0426	$168.04	$168.05	$168.00
Purchase #2	$37.70	12.322%	$42.3454	$42.35	$42.35	$42.30
Purchase #3	$155.25	4.639%	$162.452	$162.45	$162.45	$162.50
Purchase #4	$24.76	8.470%	$26.8572	$26.86	$26.85	$26.90
Purchase #5	$174.92	3.709%	$181.4078	$181.41	$181.40	$181.40
Purchase #6	$102.45	9.136%	$111.8098	$111.81	$111.80	$111.80
Purchase #7	$53.92	6.758%	$57.5639	$57.56	$57.55	$57.60
7 purchase totals =	$698.56		$750.4787	$750.48	$750.45	$750.50