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	$8.73	6.162%	$9.2679	$9.27	$9.25	$9.30
Purchase #2	$189.82	3.477%	$196.42	$196.42	$196.40	$196.40
Purchase #3	$6.58	11.278%	$7.3221	$7.32	$7.30	$7.30
Purchase #4	$179.76	5.137%	$188.9943	$188.99	$189.00	$189.00
Purchase #5	$67.92	7.277%	$72.8625	$72.86	$72.85	$72.90
Purchase #6	$174.54	3.206%	$180.1358	$180.14	$180.15	$180.10
Purchase #7	$127.52	11.770%	$142.5291	$142.53	$142.55	$142.50
7 purchase totals =	$754.87		$797.5317	$797.53	$797.50	$797.50