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	$37.52	11.456%	$41.8183	$41.82	$41.80	$41.80
Purchase #2	$120.42	12.230%	$135.1474	$135.15	$135.15	$135.10
Purchase #3	$98.84	4.265%	$103.0555	$103.06	$103.05	$103.10
Purchase #4	$152.74	10.374%	$168.5852	$168.59	$168.60	$168.60
Purchase #5	$124.45	13.734%	$141.542	$141.54	$141.55	$141.50
Purchase #6	$69.86	12.488%	$78.5841	$78.58	$78.60	$78.60
Purchase #7	$5.60	13.651%	$6.3645	$6.36	$6.35	$6.40
7 purchase totals =	$609.43		$675.0970	$675.10	$675.10	$675.10