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	$85.54	4.228%	$89.1566	$89.16	$89.15	$89.20
Purchase #2	$224.64	11.330%	$250.0917	$250.09	$250.10	$250.10
Purchase #3	$186.28	12.446%	$209.4644	$209.46	$209.45	$209.50
Purchase #4	$31.33	5.810%	$33.1503	$33.15	$33.15	$33.20
Purchase #5	$9.99	11.693%	$11.1581	$11.16	$11.15	$11.20
Purchase #6	$206.82	11.590%	$230.7904	$230.79	$230.80	$230.80
Purchase #7	$227.57	11.505%	$253.7519	$253.75	$253.75	$253.80
7 purchase totals =	$972.17		$1,077.5634	$1,077.56	$1,077.55	$1,077.80