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	$80.87	12.512%	$90.9885	$90.99	$91.00	$91.00
Purchase #2	$17.67	9.803%	$19.4022	$19.40	$19.40	$19.40
Purchase #3	$109.32	4.792%	$114.5586	$114.56	$114.55	$114.60
Purchase #4	$172.98	13.461%	$196.2648	$196.26	$196.25	$196.30
Purchase #5	$13.32	6.106%	$14.1333	$14.13	$14.15	$14.10
Purchase #6	$102.81	3.499%	$106.4073	$106.41	$106.40	$106.40
Purchase #7	$136.93	3.334%	$141.4952	$141.50	$141.50	$141.50
7 purchase totals =	$633.90		$683.2499	$683.25	$683.25	$683.30