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	$152.69	4.360%	$159.3473	$159.35	$159.35	$159.30
Purchase #2	$208.83	9.633%	$228.9466	$228.95	$228.95	$228.90
Purchase #3	$240.48	10.543%	$265.8338	$265.83	$265.85	$265.80
Purchase #4	$100.31	11.561%	$111.9068	$111.91	$111.90	$111.90
Purchase #5	$180.95	5.106%	$190.1893	$190.19	$190.20	$190.20
Purchase #6	$137.43	12.216%	$154.2184	$154.22	$154.20	$154.20
Purchase #7	$35.45	4.208%	$36.9417	$36.94	$36.95	$36.90
7 purchase totals =	$1,056.14		$1,147.3839	$1,147.39	$1,147.40	$1,147.20