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	$222.53	12.224%	$249.7321	$249.73	$249.75	$249.70
Purchase #2	$121.38	5.295%	$127.8071	$127.81	$127.80	$127.80
Purchase #3	$140.29	8.579%	$152.3255	$152.33	$152.35	$152.30
Purchase #4	$195.52	5.835%	$206.9286	$206.93	$206.95	$206.90
Purchase #5	$95.94	3.687%	$99.4773	$99.48	$99.50	$99.50
Purchase #6	$62.48	9.453%	$68.3862	$68.39	$68.40	$68.40
Purchase #7	$105.62	7.445%	$113.4834	$113.48	$113.50	$113.50
7 purchase totals =	$943.76		$1,018.1402	$1,018.15	$1,018.25	$1,018.10