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	$62.69	6.144%	$66.5417	$66.54	$66.55	$66.50
Purchase #2	$129.34	11.758%	$144.5478	$144.55	$144.55	$144.50
Purchase #3	$234.86	10.555%	$259.6495	$259.65	$259.65	$259.60
Purchase #4	$18.50	11.801%	$20.6832	$20.68	$20.70	$20.70
Purchase #5	$175.79	7.576%	$189.1079	$189.11	$189.10	$189.10
Purchase #6	$139.26	11.313%	$155.0145	$155.01	$155.00	$155.00
Purchase #7	$65.33	12.499%	$73.4956	$73.50	$73.50	$73.50
7 purchase totals =	$825.77		$909.0402	$909.04	$909.05	$908.90