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	$204.49	12.193%	$229.4235	$229.42	$229.40	$229.40
Purchase #2	$221.49	8.658%	$240.6666	$240.67	$240.65	$240.70
Purchase #3	$81.85	12.705%	$92.249	$92.25	$92.25	$92.20
Purchase #4	$131.60	4.211%	$137.1417	$137.14	$137.15	$137.10
Purchase #5	$28.89	9.742%	$31.7045	$31.70	$31.70	$31.70
Purchase #6	$184.72	7.332%	$198.2637	$198.26	$198.25	$198.30
Purchase #7	$80.55	6.387%	$85.6947	$85.69	$85.70	$85.70
7 purchase totals =	$933.59		$1,015.1437	$1,015.13	$1,015.10	$1,015.10