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	$231.39	9.395%	$253.1291	$253.13	$253.15	$253.10
Purchase #2	$137.90	9.118%	$150.4737	$150.47	$150.45	$150.50
Purchase #3	$180.90	9.469%	$198.0294	$198.03	$198.05	$198.00
Purchase #4	$219.93	7.581%	$236.6029	$236.60	$236.60	$236.60
Purchase #5	$77.26	10.743%	$85.56	$85.56	$85.55	$85.60
Purchase #6	$210.77	9.679%	$231.1704	$231.17	$231.15	$231.20
Purchase #7	$145.57	5.701%	$153.8689	$153.87	$153.85	$153.90
7 purchase totals =	$1,203.72		$1,308.8344	$1,308.83	$1,308.80	$1,308.90