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	$70.76	12.620%	$79.6899	$79.69	$79.70	$79.70
Purchase #2	$100.43	4.468%	$104.9172	$104.92	$104.90	$104.90
Purchase #3	$102.85	11.603%	$114.7837	$114.78	$114.80	$114.80
Purchase #4	$11.96	10.695%	$13.2391	$13.24	$13.25	$13.20
Purchase #5	$83.74	7.256%	$89.8162	$89.82	$89.80	$89.80
Purchase #6	$78.26	4.573%	$81.8388	$81.84	$81.85	$81.80
Purchase #7	$137.27	11.487%	$153.0382	$153.04	$153.05	$153.00
7 purchase totals =	$585.27		$637.3231	$637.33	$637.35	$637.20