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	$110.97	11.166%	$123.3609	$123.36	$123.35	$123.40
Purchase #2	$96.52	4.190%	$100.5642	$100.56	$100.55	$100.60
Purchase #3	$132.66	11.280%	$147.624	$147.62	$147.60	$147.60
Purchase #4	$21.96	9.218%	$23.9843	$23.98	$24.00	$24.00
Purchase #5	$111.33	11.630%	$124.2777	$124.28	$124.30	$124.30
Purchase #6	$100.99	4.550%	$105.585	$105.59	$105.60	$105.60
Purchase #7	$115.25	3.488%	$119.2699	$119.27	$119.25	$119.30
7 purchase totals =	$689.68		$744.6660	$744.66	$744.65	$744.80