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	$81.75	10.137%	$90.037	$90.04	$90.05	$90.00
Purchase #2	$16.78	4.572%	$17.5472	$17.55	$17.55	$17.50
Purchase #3	$245.34	7.541%	$263.8411	$263.84	$263.85	$263.80
Purchase #4	$133.83	6.803%	$142.9345	$142.93	$142.95	$142.90
Purchase #5	$112.95	9.677%	$123.8802	$123.88	$123.90	$123.90
Purchase #6	$63.39	13.154%	$71.7283	$71.73	$71.75	$71.70
Purchase #7	$59.44	5.781%	$62.8762	$62.88	$62.90	$62.90
7 purchase totals =	$713.48		$772.8445	$772.85	$772.95	$772.70