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	$37.89	10.245%	$41.7718	$41.77	$41.75	$41.80
Purchase #2	$79.32	12.566%	$89.2874	$89.29	$89.30	$89.30
Purchase #3	$78.86	7.213%	$84.5482	$84.55	$84.55	$84.50
Purchase #4	$58.44	12.778%	$65.9075	$65.91	$65.90	$65.90
Purchase #5	$210.61	3.853%	$218.7248	$218.72	$218.70	$218.70
Purchase #6	$95.71	12.103%	$107.2938	$107.29	$107.30	$107.30
Purchase #7	$211.67	3.871%	$219.8637	$219.86	$219.85	$219.90
7 purchase totals =	$772.50		$827.3972	$827.39	$827.35	$827.40