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	$91.25	10.224%	$100.5794	$100.58	$100.60	$100.60
Purchase #2	$183.45	8.365%	$198.7956	$198.80	$198.80	$198.80
Purchase #3	$80.52	10.310%	$88.8216	$88.82	$88.80	$88.80
Purchase #4	$164.77	8.799%	$179.2681	$179.27	$179.25	$179.30
Purchase #5	$119.33	3.443%	$123.4385	$123.44	$123.45	$123.40
Purchase #6	$63.94	5.265%	$67.3064	$67.31	$67.30	$67.30
Purchase #7	$109.67	10.451%	$121.1316	$121.13	$121.15	$121.10
7 purchase totals =	$812.93		$879.3412	$879.35	$879.35	$879.30