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	$39.25	9.220%	$42.8689	$42.87	$42.85	$42.90
Purchase #2	$72.86	8.773%	$79.252	$79.25	$79.25	$79.30
Purchase #3	$218.86	3.218%	$225.9029	$225.90	$225.90	$225.90
Purchase #4	$178.45	6.198%	$189.5103	$189.51	$189.50	$189.50
Purchase #5	$65.64	10.760%	$72.7029	$72.70	$72.70	$72.70
Purchase #6	$109.64	7.236%	$117.5736	$117.57	$117.55	$117.60
Purchase #7	$223.47	8.561%	$242.6013	$242.60	$242.60	$242.60
7 purchase totals =	$908.17		$970.4119	$970.40	$970.35	$970.50