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	$19.29	10.439%	$21.3037	$21.30	$21.30	$21.30
Purchase #2	$213.37	11.757%	$238.4559	$238.46	$238.45	$238.50
Purchase #3	$206.80	4.423%	$215.9468	$215.95	$215.95	$215.90
Purchase #4	$218.98	10.153%	$241.213	$241.21	$241.20	$241.20
Purchase #5	$48.41	4.439%	$50.5589	$50.56	$50.55	$50.60
Purchase #6	$151.78	11.837%	$169.7462	$169.75	$169.75	$169.70
Purchase #7	$139.29	3.516%	$144.1874	$144.19	$144.20	$144.20
7 purchase totals =	$997.92		$1,081.4119	$1,081.42	$1,081.40	$1,081.40