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	$236.33	13.387%	$267.9675	$267.97	$267.95	$268.00
Purchase #2	$123.71	11.149%	$137.5024	$137.50	$137.50	$137.50
Purchase #3	$133.97	13.108%	$151.5308	$151.53	$151.55	$151.50
Purchase #4	$25.97	11.439%	$28.9407	$28.94	$28.95	$28.90
Purchase #5	$99.69	9.276%	$108.9372	$108.94	$108.95	$108.90
Purchase #6	$139.94	8.874%	$152.3583	$152.36	$152.35	$152.40
Purchase #7	$172.68	6.774%	$184.3773	$184.38	$184.40	$184.40
7 purchase totals =	$932.29		$1,031.6142	$1,031.62	$1,031.65	$1,031.60