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	$37.62	3.863%	$39.0733	$39.07	$39.05	$39.10
Purchase #2	$127.44	9.284%	$139.2715	$139.27	$139.25	$139.30
Purchase #3	$33.75	6.781%	$36.0386	$36.04	$36.05	$36.00
Purchase #4	$65.72	10.425%	$72.5713	$72.57	$72.55	$72.60
Purchase #5	$59.69	3.765%	$61.9373	$61.94	$61.95	$61.90
Purchase #6	$63.59	5.203%	$66.8986	$66.90	$66.90	$66.90
Purchase #7	$79.60	8.410%	$86.2944	$86.29	$86.30	$86.30
7 purchase totals =	$467.41		$502.0850	$502.08	$502.05	$502.10