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	$215.58	10.129%	$237.4161	$237.42	$237.40	$237.40
Purchase #2	$236.56	8.237%	$256.0454	$256.05	$256.05	$256.00
Purchase #3	$115.29	7.672%	$124.135	$124.14	$124.15	$124.10
Purchase #4	$75.26	13.465%	$85.3938	$85.39	$85.40	$85.40
Purchase #5	$80.75	11.177%	$89.7754	$89.78	$89.80	$89.80
Purchase #6	$180.81	10.802%	$200.3411	$200.34	$200.35	$200.30
Purchase #7	$25.50	7.669%	$27.4556	$27.46	$27.45	$27.50
7 purchase totals =	$929.75		$1,020.5624	$1,020.58	$1,020.60	$1,020.50