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	$92.66	11.394%	$103.2177	$103.22	$103.20	$103.20
Purchase #2	$179.92	9.197%	$196.4672	$196.47	$196.45	$196.50
Purchase #3	$58.69	10.526%	$64.8677	$64.87	$64.85	$64.90
Purchase #4	$10.29	7.679%	$11.0802	$11.08	$11.10	$11.10
Purchase #5	$190.89	13.445%	$216.5552	$216.56	$216.55	$216.60
Purchase #6	$156.46	7.365%	$167.9833	$167.98	$168.00	$168.00
Purchase #7	$121.39	6.476%	$129.2512	$129.25	$129.25	$129.30
7 purchase totals =	$810.30		$889.4225	$889.43	$889.40	$889.60