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	$135.32	4.849%	$141.8817	$141.88	$141.90	$141.90
Purchase #2	$38.53	6.644%	$41.0899	$41.09	$41.10	$41.10
Purchase #3	$11.50	9.257%	$12.5646	$12.56	$12.55	$12.60
Purchase #4	$136.95	10.371%	$151.1531	$151.15	$151.15	$151.20
Purchase #5	$175.42	10.740%	$194.2601	$194.26	$194.25	$194.30
Purchase #6	$144.78	3.690%	$150.1224	$150.12	$150.10	$150.10
Purchase #7	$20.42	4.483%	$21.3354	$21.34	$21.35	$21.30
7 purchase totals =	$662.92		$712.4072	$712.40	$712.40	$712.50