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	$61.40	6.690%	$65.5077	$65.51	$65.50	$65.50
Purchase #2	$249.64	5.165%	$262.5339	$262.53	$262.55	$262.50
Purchase #3	$63.82	5.848%	$67.5522	$67.55	$67.55	$67.60
Purchase #4	$90.64	11.349%	$100.9267	$100.93	$100.95	$100.90
Purchase #5	$148.93	4.470%	$155.5872	$155.59	$155.60	$155.60
Purchase #6	$19.38	7.700%	$20.8723	$20.87	$20.85	$20.90
Purchase #7	$185.73	11.123%	$206.3887	$206.39	$206.40	$206.40
7 purchase totals =	$819.54		$879.3687	$879.37	$879.40	$879.40