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	$199.66	10.331%	$220.2869	$220.29	$220.30	$220.30
Purchase #2	$72.77	7.710%	$78.3806	$78.38	$78.40	$78.40
Purchase #3	$158.90	8.524%	$172.4446	$172.44	$172.45	$172.40
Purchase #4	$163.59	12.686%	$184.343	$184.34	$184.35	$184.30
Purchase #5	$247.71	4.236%	$258.203	$258.20	$258.20	$258.20
Purchase #6	$168.94	12.670%	$190.3447	$190.34	$190.35	$190.30
Purchase #7	$10.55	8.847%	$11.4834	$11.48	$11.50	$11.50
7 purchase totals =	$1,022.12		$1,115.4862	$1,115.47	$1,115.55	$1,115.40