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	$169.46	12.567%	$190.756	$190.76	$190.75	$190.80
Purchase #2	$170.60	9.122%	$186.1621	$186.16	$186.15	$186.20
Purchase #3	$115.88	6.571%	$123.4945	$123.49	$123.50	$123.50
Purchase #4	$170.49	10.534%	$188.4494	$188.45	$188.45	$188.40
Purchase #5	$52.25	8.321%	$56.5977	$56.60	$56.60	$56.60
Purchase #6	$100.56	7.747%	$108.3504	$108.35	$108.35	$108.40
Purchase #7	$71.88	13.322%	$81.4559	$81.46	$81.45	$81.50
7 purchase totals =	$851.12		$935.2660	$935.27	$935.25	$935.40