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	$146.68	13.780%	$166.8925	$166.89	$166.90	$166.90
Purchase #2	$139.68	4.359%	$145.7687	$145.77	$145.75	$145.80
Purchase #3	$39.43	13.839%	$44.8867	$44.89	$44.90	$44.90
Purchase #4	$142.38	11.768%	$159.1353	$159.14	$159.15	$159.10
Purchase #5	$131.84	6.317%	$140.1683	$140.17	$140.15	$140.20
Purchase #6	$193.76	5.744%	$204.8896	$204.89	$204.90	$204.90
Purchase #7	$86.67	3.277%	$89.5102	$89.51	$89.50	$89.50
7 purchase totals =	$880.44		$951.2513	$951.26	$951.25	$951.30