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	$58.98	7.281%	$63.2743	$63.27	$63.25	$63.30
Purchase #2	$42.93	12.430%	$48.2662	$48.27	$48.25	$48.30
Purchase #3	$197.38	12.873%	$222.7887	$222.79	$222.80	$222.80
Purchase #4	$124.74	5.650%	$131.7878	$131.79	$131.80	$131.80
Purchase #5	$166.48	11.467%	$185.5703	$185.57	$185.55	$185.60
Purchase #6	$92.47	3.157%	$95.3893	$95.39	$95.40	$95.40
Purchase #7	$228.53	6.250%	$242.8131	$242.81	$242.80	$242.80
7 purchase totals =	$911.51		$989.8897	$989.89	$989.85	$990.00