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	$166.29	10.848%	$184.3291	$184.33	$184.35	$184.30
Purchase #2	$99.89	6.386%	$106.269	$106.27	$106.25	$106.30
Purchase #3	$86.46	3.871%	$89.8069	$89.81	$89.80	$89.80
Purchase #4	$139.42	12.250%	$156.499	$156.50	$156.50	$156.50
Purchase #5	$103.63	11.209%	$115.2459	$115.25	$115.25	$115.20
Purchase #6	$131.47	7.439%	$141.2501	$141.25	$141.25	$141.30
Purchase #7	$47.49	4.420%	$49.5891	$49.59	$49.60	$49.60
7 purchase totals =	$774.65		$842.9891	$843.00	$843.00	$843.00