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	$52.68	12.827%	$59.4373	$59.44	$59.45	$59.40
Purchase #2	$28.54	8.198%	$30.8797	$30.88	$30.90	$30.90
Purchase #3	$245.83	8.455%	$266.6149	$266.61	$266.60	$266.60
Purchase #4	$54.63	7.314%	$58.6256	$58.63	$58.65	$58.60
Purchase #5	$73.47	6.616%	$78.3308	$78.33	$78.35	$78.30
Purchase #6	$157.84	10.535%	$174.4684	$174.47	$174.45	$174.50
Purchase #7	$114.65	7.868%	$123.6707	$123.67	$123.65	$123.70
7 purchase totals =	$727.64		$792.0274	$792.03	$792.05	$792.00