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	$89.29	12.553%	$100.4986	$100.50	$100.50	$100.50
Purchase #2	$235.66	10.831%	$261.1843	$261.18	$261.20	$261.20
Purchase #3	$172.91	5.376%	$182.2056	$182.21	$182.20	$182.20
Purchase #4	$198.27	4.321%	$206.8372	$206.84	$206.85	$206.80
Purchase #5	$142.43	6.428%	$151.5854	$151.59	$151.60	$151.60
Purchase #6	$41.90	9.425%	$45.8491	$45.85	$45.85	$45.80
Purchase #7	$37.65	9.752%	$41.3216	$41.32	$41.30	$41.30
7 purchase totals =	$918.11		$989.4818	$989.49	$989.50	$989.40