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	$100.27	5.850%	$106.1358	$106.14	$106.15	$106.10
Purchase #2	$67.60	5.108%	$71.053	$71.05	$71.05	$71.10
Purchase #3	$162.53	5.732%	$171.8462	$171.85	$171.85	$171.80
Purchase #4	$70.59	8.819%	$76.8153	$76.82	$76.80	$76.80
Purchase #5	$156.34	4.788%	$163.8256	$163.83	$163.85	$163.80
Purchase #6	$155.81	4.256%	$162.4413	$162.44	$162.45	$162.40
Purchase #7	$130.33	6.855%	$139.2641	$139.26	$139.25	$139.30
7 purchase totals =	$843.47		$891.3813	$891.39	$891.40	$891.30