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	$234.40	3.596%	$242.829	$242.83	$242.85	$242.80
Purchase #2	$226.28	8.260%	$244.9707	$244.97	$244.95	$245.00
Purchase #3	$104.74	10.216%	$115.4402	$115.44	$115.45	$115.40
Purchase #4	$95.93	5.105%	$100.8272	$100.83	$100.85	$100.80
Purchase #5	$126.76	8.814%	$137.9326	$137.93	$137.95	$137.90
Purchase #6	$245.45	10.189%	$270.4589	$270.46	$270.45	$270.50
Purchase #7	$89.77	10.477%	$99.1752	$99.18	$99.20	$99.20
7 purchase totals =	$1,123.33		$1,211.6338	$1,211.64	$1,211.70	$1,211.60