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	$39.79	5.434%	$41.9522	$41.95	$41.95	$42.00
Purchase #2	$86.45	5.330%	$91.0578	$91.06	$91.05	$91.10
Purchase #3	$207.38	9.500%	$227.0811	$227.08	$227.10	$227.10
Purchase #4	$106.32	5.230%	$111.8805	$111.88	$111.90	$111.90
Purchase #5	$6.93	13.650%	$7.8759	$7.88	$7.90	$7.90
Purchase #6	$38.97	11.502%	$43.4523	$43.45	$43.45	$43.50
Purchase #7	$151.41	9.489%	$165.7773	$165.78	$165.80	$165.80
7 purchase totals =	$637.25		$689.0771	$689.08	$689.15	$689.30