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	$204.62	12.204%	$229.5918	$229.59	$229.60	$229.60
Purchase #2	$160.76	5.225%	$169.1597	$169.16	$169.15	$169.20
Purchase #3	$85.63	4.791%	$89.7325	$89.73	$89.75	$89.70
Purchase #4	$158.45	6.701%	$169.0677	$169.07	$169.05	$169.10
Purchase #5	$5.27	4.703%	$5.5178	$5.52	$5.50	$5.50
Purchase #6	$93.86	11.782%	$104.9186	$104.92	$104.90	$104.90
Purchase #7	$29.46	11.735%	$32.9171	$32.92	$32.90	$32.90
7 purchase totals =	$738.05		$800.9052	$800.91	$800.85	$800.90