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	$28.48	4.859%	$29.8638	$29.86	$29.85	$29.90
Purchase #2	$78.30	5.558%	$82.6519	$82.65	$82.65	$82.70
Purchase #3	$244.38	12.221%	$274.2457	$274.25	$274.25	$274.20
Purchase #4	$46.86	8.412%	$50.8019	$50.80	$50.80	$50.80
Purchase #5	$97.69	6.776%	$104.3095	$104.31	$104.30	$104.30
Purchase #6	$110.30	4.383%	$115.1344	$115.13	$115.15	$115.10
Purchase #7	$199.35	9.788%	$218.8624	$218.86	$218.85	$218.90
7 purchase totals =	$805.36		$875.8696	$875.86	$875.85	$875.90