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	$109.51	6.149%	$116.2438	$116.24	$116.25	$116.20
Purchase #2	$47.44	4.143%	$49.4054	$49.41	$49.40	$49.40
Purchase #3	$182.76	12.415%	$205.4497	$205.45	$205.45	$205.40
Purchase #4	$16.31	10.803%	$18.072	$18.07	$18.05	$18.10
Purchase #5	$150.56	8.196%	$162.8999	$162.90	$162.90	$162.90
Purchase #6	$219.56	9.701%	$240.8595	$240.86	$240.85	$240.90
Purchase #7	$199.50	11.562%	$222.5662	$222.57	$222.55	$222.60
7 purchase totals =	$925.64		$1,015.4965	$1,015.50	$1,015.45	$1,015.50