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	$97.60	12.661%	$109.9571	$109.96	$109.95	$110.00
Purchase #2	$100.38	12.441%	$112.8683	$112.87	$112.85	$112.90
Purchase #3	$165.43	8.264%	$179.1011	$179.10	$179.10	$179.10
Purchase #4	$153.52	12.597%	$172.8589	$172.86	$172.85	$172.90
Purchase #5	$117.48	10.645%	$129.9857	$129.99	$130.00	$130.00
Purchase #6	$22.36	10.283%	$24.6593	$24.66	$24.65	$24.70
Purchase #7	$53.85	10.422%	$59.4622	$59.46	$59.45	$59.50
7 purchase totals =	$710.62		$788.8926	$788.90	$788.85	$789.10