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	$136.42	11.842%	$152.5749	$152.57	$152.55	$152.60
Purchase #2	$181.59	8.313%	$196.6856	$196.69	$196.70	$196.70
Purchase #3	$100.95	3.306%	$104.2874	$104.29	$104.30	$104.30
Purchase #4	$134.93	9.517%	$147.7713	$147.77	$147.75	$147.80
Purchase #5	$86.48	6.184%	$91.8279	$91.83	$91.85	$91.80
Purchase #6	$59.87	6.308%	$63.6466	$63.65	$63.65	$63.60
Purchase #7	$99.73	3.465%	$103.1856	$103.19	$103.20	$103.20
7 purchase totals =	$799.97		$859.9793	$859.99	$860.00	$860.00