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	$104.38	10.522%	$115.3629	$115.36	$115.35	$115.40
Purchase #2	$82.80	9.441%	$90.6171	$90.62	$90.60	$90.60
Purchase #3	$139.94	4.507%	$146.2471	$146.25	$146.25	$146.20
Purchase #4	$63.71	11.370%	$70.9538	$70.95	$70.95	$71.00
Purchase #5	$115.45	11.572%	$128.8099	$128.81	$128.80	$128.80
Purchase #6	$76.27	5.849%	$80.731	$80.73	$80.75	$80.70
Purchase #7	$127.64	10.656%	$141.2413	$141.24	$141.25	$141.20
7 purchase totals =	$710.19		$773.9631	$773.96	$773.95	$773.90