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	$147.52	12.518%	$165.9866	$165.99	$166.00	$166.00
Purchase #2	$104.69	10.253%	$115.4239	$115.42	$115.40	$115.40
Purchase #3	$90.71	4.561%	$94.8473	$94.85	$94.85	$94.80
Purchase #4	$206.76	12.576%	$232.7621	$232.76	$232.75	$232.80
Purchase #5	$157.77	4.458%	$164.8034	$164.80	$164.80	$164.80
Purchase #6	$54.77	8.534%	$59.4441	$59.44	$59.45	$59.40
Purchase #7	$105.88	7.569%	$113.8941	$113.89	$113.90	$113.90
7 purchase totals =	$868.10		$947.1615	$947.15	$947.15	$947.10