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	$96.35	13.138%	$109.0085	$109.01	$109.00	$109.00
Purchase #2	$98.39	11.285%	$109.4933	$109.49	$109.50	$109.50
Purchase #3	$150.68	10.473%	$166.4607	$166.46	$166.45	$166.50
Purchase #4	$112.84	6.395%	$120.0561	$120.06	$120.05	$120.10
Purchase #5	$190.41	8.329%	$206.2692	$206.27	$206.25	$206.30
Purchase #6	$54.90	11.460%	$61.1915	$61.19	$61.20	$61.20
Purchase #7	$42.72	13.498%	$48.4863	$48.49	$48.50	$48.50
7 purchase totals =	$746.29		$820.9656	$820.97	$820.95	$821.10