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	$158.57	8.173%	$171.5299	$171.53	$171.55	$171.50
Purchase #2	$213.79	11.295%	$237.9376	$237.94	$237.95	$237.90
Purchase #3	$64.88	10.500%	$71.6924	$71.69	$71.70	$71.70
Purchase #4	$89.32	11.341%	$99.4498	$99.45	$99.45	$99.40
Purchase #5	$48.38	8.735%	$52.606	$52.61	$52.60	$52.60
Purchase #6	$82.93	8.862%	$90.2793	$90.28	$90.30	$90.30
Purchase #7	$82.85	5.647%	$87.5285	$87.53	$87.55	$87.50
7 purchase totals =	$740.72		$811.0235	$811.03	$811.10	$810.90