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	$37.32	13.661%	$42.4183	$42.42	$42.40	$42.40
Purchase #2	$52.31	3.137%	$53.951	$53.95	$53.95	$54.00
Purchase #3	$45.33	6.605%	$48.324	$48.32	$48.30	$48.30
Purchase #4	$198.44	9.468%	$217.2283	$217.23	$217.25	$217.20
Purchase #5	$157.85	6.765%	$168.5286	$168.53	$168.55	$168.50
Purchase #6	$150.51	11.316%	$167.5417	$167.54	$167.55	$167.50
Purchase #7	$124.81	10.830%	$138.3269	$138.33	$138.35	$138.30
7 purchase totals =	$766.57		$836.3188	$836.32	$836.35	$836.20