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	$76.67	8.132%	$82.9048	$82.90	$82.90	$82.90
Purchase #2	$46.68	13.557%	$53.0084	$53.01	$53.00	$53.00
Purchase #3	$113.71	8.511%	$123.3879	$123.39	$123.40	$123.40
Purchase #4	$100.76	11.506%	$112.3534	$112.35	$112.35	$112.40
Purchase #5	$190.40	10.605%	$210.5919	$210.59	$210.60	$210.60
Purchase #6	$16.93	4.133%	$17.6297	$17.63	$17.65	$17.60
Purchase #7	$6.91	11.416%	$7.6988	$7.70	$7.70	$7.70
7 purchase totals =	$552.06		$607.5749	$607.57	$607.60	$607.60