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	$49.33	6.559%	$52.5656	$52.57	$52.55	$52.60
Purchase #2	$113.31	8.221%	$122.6252	$122.63	$122.65	$122.60
Purchase #3	$79.70	13.560%	$90.5073	$90.51	$90.50	$90.50
Purchase #4	$115.82	6.641%	$123.5116	$123.51	$123.50	$123.50
Purchase #5	$104.89	5.329%	$110.4796	$110.48	$110.50	$110.50
Purchase #6	$77.87	7.123%	$83.4167	$83.42	$83.40	$83.40
Purchase #7	$40.59	3.872%	$42.1616	$42.16	$42.15	$42.20
7 purchase totals =	$581.51		$625.2676	$625.28	$625.25	$625.30