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	$145.83	13.772%	$165.9137	$165.91	$165.90	$165.90
Purchase #2	$148.53	12.254%	$166.7309	$166.73	$166.75	$166.70
Purchase #3	$201.82	13.858%	$229.7882	$229.79	$229.80	$229.80
Purchase #4	$102.41	10.276%	$112.9337	$112.93	$112.95	$112.90
Purchase #5	$58.62	4.820%	$61.4455	$61.45	$61.45	$61.40
Purchase #6	$115.35	4.314%	$120.3262	$120.33	$120.35	$120.30
Purchase #7	$54.40	13.256%	$61.6113	$61.61	$61.60	$61.60
7 purchase totals =	$826.96		$918.7495	$918.75	$918.80	$918.60