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	$28.79	9.509%	$31.5276	$31.53	$31.55	$31.50
Purchase #2	$31.97	11.363%	$35.6028	$35.60	$35.60	$35.60
Purchase #3	$162.90	7.596%	$175.2739	$175.27	$175.25	$175.30
Purchase #4	$208.52	13.150%	$235.9404	$235.94	$235.95	$235.90
Purchase #5	$186.33	6.661%	$198.7414	$198.74	$198.75	$198.70
Purchase #6	$146.30	8.469%	$158.6901	$158.69	$158.70	$158.70
Purchase #7	$225.85	13.340%	$255.9784	$255.98	$256.00	$256.00
7 purchase totals =	$990.66		$1,091.7546	$1,091.75	$1,091.80	$1,091.70