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	$233.29	4.321%	$243.3705	$243.37	$243.35	$243.40
Purchase #2	$131.70	6.310%	$140.0103	$140.01	$140.00	$140.00
Purchase #3	$212.61	13.169%	$240.6086	$240.61	$240.60	$240.60
Purchase #4	$69.47	6.849%	$74.228	$74.23	$74.25	$74.20
Purchase #5	$28.88	9.350%	$31.5803	$31.58	$31.60	$31.60
Purchase #6	$232.86	9.202%	$254.2878	$254.29	$254.30	$254.30
Purchase #7	$128.59	8.404%	$139.3967	$139.40	$139.40	$139.40
7 purchase totals =	$1,037.40		$1,123.4822	$1,123.49	$1,123.50	$1,123.50