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	$133.31	12.784%	$150.3524	$150.35	$150.35	$150.40
Purchase #2	$242.50	6.693%	$258.7305	$258.73	$258.75	$258.70
Purchase #3	$90.35	10.404%	$99.75	$99.75	$99.75	$99.80
Purchase #4	$154.98	9.396%	$169.5419	$169.54	$169.55	$169.50
Purchase #5	$135.63	5.681%	$143.3351	$143.34	$143.35	$143.30
Purchase #6	$202.55	12.751%	$228.3772	$228.38	$228.40	$228.40
Purchase #7	$68.83	4.716%	$72.076	$72.08	$72.10	$72.10
7 purchase totals =	$1,028.15		$1,122.1631	$1,122.17	$1,122.25	$1,122.20