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	$38.95	3.145%	$40.175	$40.18	$40.20	$40.20
Purchase #2	$240.92	10.372%	$265.9082	$265.91	$265.90	$265.90
Purchase #3	$164.91	13.750%	$187.5851	$187.59	$187.60	$187.60
Purchase #4	$184.64	6.255%	$196.1892	$196.19	$196.20	$196.20
Purchase #5	$100.25	6.654%	$106.9206	$106.92	$106.90	$106.90
Purchase #6	$152.47	4.524%	$159.3677	$159.37	$159.35	$159.40
Purchase #7	$72.69	7.666%	$78.2624	$78.26	$78.25	$78.30
7 purchase totals =	$954.83		$1,034.4082	$1,034.42	$1,034.40	$1,034.50