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	$142.37	3.306%	$147.0768	$147.08	$147.10	$147.10
Purchase #2	$48.77	13.560%	$55.3832	$55.38	$55.40	$55.40
Purchase #3	$141.90	9.501%	$155.3819	$155.38	$155.40	$155.40
Purchase #4	$177.99	10.628%	$196.9068	$196.91	$196.90	$196.90
Purchase #5	$78.33	6.265%	$83.2374	$83.24	$83.25	$83.20
Purchase #6	$78.50	11.452%	$87.4898	$87.49	$87.50	$87.50
Purchase #7	$233.40	10.467%	$257.83	$257.83	$257.85	$257.80
7 purchase totals =	$901.26		$983.3059	$983.31	$983.40	$983.30