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	$36.25	10.448%	$40.0374	$40.04	$40.05	$40.00
Purchase #2	$119.88	6.651%	$127.8532	$127.85	$127.85	$127.90
Purchase #3	$90.38	5.431%	$95.2885	$95.29	$95.30	$95.30
Purchase #4	$42.40	12.481%	$47.6919	$47.69	$47.70	$47.70
Purchase #5	$120.85	6.803%	$129.0714	$129.07	$129.05	$129.10
Purchase #6	$55.94	7.166%	$59.9487	$59.95	$59.95	$59.90
Purchase #7	$68.50	7.660%	$73.7471	$73.75	$73.75	$73.70
7 purchase totals =	$534.20		$573.6382	$573.64	$573.65	$573.60