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	$39.73	3.533%	$41.1337	$41.13	$41.15	$41.10
Purchase #2	$217.89	6.391%	$231.8153	$231.82	$231.80	$231.80
Purchase #3	$77.60	6.697%	$82.7969	$82.80	$82.80	$82.80
Purchase #4	$207.49	9.482%	$227.1642	$227.16	$227.15	$227.20
Purchase #5	$91.86	4.453%	$95.9505	$95.95	$95.95	$96.00
Purchase #6	$33.34	12.452%	$37.4915	$37.49	$37.50	$37.50
Purchase #7	$120.82	13.812%	$137.5077	$137.51	$137.50	$137.50
7 purchase totals =	$788.73		$853.8598	$853.86	$853.85	$853.90