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	$72.43	9.239%	$79.1218	$79.12	$79.10	$79.10
Purchase #2	$204.66	12.764%	$230.7828	$230.78	$230.80	$230.80
Purchase #3	$99.43	6.589%	$105.9814	$105.98	$106.00	$106.00
Purchase #4	$88.83	7.829%	$95.7845	$95.78	$95.80	$95.80
Purchase #5	$79.44	12.300%	$89.2111	$89.21	$89.20	$89.20
Purchase #6	$31.57	3.150%	$32.5645	$32.56	$32.55	$32.60
Purchase #7	$30.28	5.125%	$31.8319	$31.83	$31.85	$31.80
7 purchase totals =	$606.64		$665.2780	$665.26	$665.30	$665.30