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	$64.89	9.118%	$70.8067	$70.81	$70.80	$70.80
Purchase #2	$214.49	7.809%	$231.2395	$231.24	$231.25	$231.20
Purchase #3	$131.51	4.111%	$136.9164	$136.92	$136.90	$136.90
Purchase #4	$78.61	13.575%	$89.2813	$89.28	$89.30	$89.30
Purchase #5	$63.70	3.360%	$65.8403	$65.84	$65.85	$65.80
Purchase #6	$222.43	10.533%	$245.8586	$245.86	$245.85	$245.90
Purchase #7	$88.54	7.787%	$95.4346	$95.43	$95.45	$95.40
7 purchase totals =	$864.17		$935.3774	$935.38	$935.40	$935.30