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	$7.88	11.568%	$8.7916	$8.79	$8.80	$8.80
Purchase #2	$103.66	7.373%	$111.3029	$111.30	$111.30	$111.30
Purchase #3	$86.26	3.231%	$89.0471	$89.05	$89.05	$89.00
Purchase #4	$39.73	7.466%	$42.6962	$42.70	$42.70	$42.70
Purchase #5	$141.44	13.105%	$159.9757	$159.98	$160.00	$160.00
Purchase #6	$116.51	3.231%	$120.2744	$120.27	$120.25	$120.30
Purchase #7	$90.41	4.525%	$94.5011	$94.50	$94.50	$94.50
7 purchase totals =	$585.89		$626.5890	$626.59	$626.60	$626.60