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	$34.53	9.376%	$37.7675	$37.77	$37.75	$37.80
Purchase #2	$232.56	4.566%	$243.1787	$243.18	$243.20	$243.20
Purchase #3	$21.64	3.245%	$22.3422	$22.34	$22.35	$22.30
Purchase #4	$46.47	6.368%	$49.4292	$49.43	$49.45	$49.40
Purchase #5	$37.84	10.108%	$41.6649	$41.66	$41.65	$41.70
Purchase #6	$145.54	9.863%	$159.8946	$159.89	$159.90	$159.90
Purchase #7	$36.44	11.342%	$40.573	$40.57	$40.55	$40.60
7 purchase totals =	$555.02		$594.8501	$594.84	$594.85	$594.90