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	$37.83	12.450%	$42.5398	$42.54	$42.55	$42.50
Purchase #2	$146.76	7.430%	$157.6643	$157.66	$157.65	$157.70
Purchase #3	$8.93	10.645%	$9.8806	$9.88	$9.90	$9.90
Purchase #4	$131.46	8.431%	$142.5434	$142.54	$142.55	$142.50
Purchase #5	$8.89	8.188%	$9.6179	$9.62	$9.60	$9.60
Purchase #6	$41.78	4.770%	$43.7729	$43.77	$43.75	$43.80
Purchase #7	$55.96	10.615%	$61.9002	$61.90	$61.90	$61.90
7 purchase totals =	$431.61		$467.9191	$467.91	$467.90	$467.90