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	$31.94	12.158%	$35.8233	$35.82	$35.80	$35.80
Purchase #2	$187.59	9.312%	$205.0584	$205.06	$205.05	$205.10
Purchase #3	$231.89	10.253%	$255.6657	$255.67	$255.65	$255.70
Purchase #4	$227.85	11.520%	$254.0983	$254.10	$254.10	$254.10
Purchase #5	$66.61	9.390%	$72.8647	$72.86	$72.85	$72.90
Purchase #6	$42.77	9.365%	$46.7754	$46.78	$46.80	$46.80
Purchase #7	$64.50	5.574%	$68.0952	$68.10	$68.10	$68.10
7 purchase totals =	$853.15		$938.3810	$938.39	$938.35	$938.50