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	$75.96	3.367%	$78.5176	$78.52	$78.50	$78.50
Purchase #2	$74.94	10.188%	$82.5749	$82.57	$82.55	$82.60
Purchase #3	$117.85	8.814%	$128.2373	$128.24	$128.25	$128.20
Purchase #4	$91.80	13.587%	$104.2729	$104.27	$104.25	$104.30
Purchase #5	$184.91	10.622%	$204.5511	$204.55	$204.55	$204.60
Purchase #6	$144.31	13.469%	$163.7471	$163.75	$163.75	$163.70
Purchase #7	$96.56	3.161%	$99.6123	$99.61	$99.60	$99.60
7 purchase totals =	$786.33		$861.5132	$861.51	$861.45	$861.50