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	$129.59	9.496%	$141.8959	$141.90	$141.90	$141.90
Purchase #2	$61.86	4.709%	$64.773	$64.77	$64.75	$64.80
Purchase #3	$98.69	5.301%	$103.9216	$103.92	$103.90	$103.90
Purchase #4	$71.85	7.242%	$77.0534	$77.05	$77.05	$77.10
Purchase #5	$134.50	7.451%	$144.5216	$144.52	$144.50	$144.50
Purchase #6	$26.91	7.283%	$28.8699	$28.87	$28.85	$28.90
Purchase #7	$41.76	9.743%	$45.8287	$45.83	$45.85	$45.80
7 purchase totals =	$565.16		$606.8641	$606.86	$606.80	$606.90