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	$40.90	3.331%	$42.2624	$42.26	$42.25	$42.30
Purchase #2	$109.83	13.157%	$124.2803	$124.28	$124.30	$124.30
Purchase #3	$76.52	11.525%	$85.3389	$85.34	$85.35	$85.30
Purchase #4	$146.91	9.606%	$161.0222	$161.02	$161.00	$161.00
Purchase #5	$130.51	8.810%	$142.0079	$142.01	$142.00	$142.00
Purchase #6	$8.34	7.523%	$8.9674	$8.97	$8.95	$9.00
Purchase #7	$86.47	4.421%	$90.2928	$90.29	$90.30	$90.30
7 purchase totals =	$599.48		$654.1719	$654.17	$654.15	$654.20