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	$102.45	3.380%	$105.9128	$105.91	$105.90	$105.90
Purchase #2	$32.36	7.686%	$34.8472	$34.85	$34.85	$34.80
Purchase #3	$124.65	7.763%	$134.3266	$134.33	$134.35	$134.30
Purchase #4	$79.78	12.650%	$89.8722	$89.87	$89.85	$89.90
Purchase #5	$31.60	4.150%	$32.9114	$32.91	$32.90	$32.90
Purchase #6	$236.39	5.415%	$249.1905	$249.19	$249.20	$249.20
Purchase #7	$33.89	12.559%	$38.1462	$38.15	$38.15	$38.10
7 purchase totals =	$641.12		$685.2069	$685.21	$685.20	$685.10