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	$47.79	4.131%	$49.7642	$49.76	$49.75	$49.80
Purchase #2	$96.90	3.518%	$100.3089	$100.31	$100.30	$100.30
Purchase #3	$128.46	5.503%	$135.5292	$135.53	$135.55	$135.50
Purchase #4	$209.83	7.393%	$225.3427	$225.34	$225.35	$225.30
Purchase #5	$20.83	3.677%	$21.5959	$21.60	$21.60	$21.60
Purchase #6	$139.51	12.406%	$156.8176	$156.82	$156.80	$156.80
Purchase #7	$161.72	6.652%	$172.4776	$172.48	$172.50	$172.50
7 purchase totals =	$805.04		$861.8361	$861.84	$861.85	$861.80