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	$55.89	5.863%	$59.1668	$59.17	$59.15	$59.20
Purchase #2	$57.70	12.463%	$64.8912	$64.89	$64.90	$64.90
Purchase #3	$24.36	12.838%	$27.4873	$27.49	$27.50	$27.50
Purchase #4	$90.35	9.800%	$99.2043	$99.20	$99.20	$99.20
Purchase #5	$155.77	5.694%	$164.6395	$164.64	$164.65	$164.60
Purchase #6	$38.97	5.198%	$40.9957	$41.00	$41.00	$41.00
Purchase #7	$7.91	12.574%	$8.9046	$8.90	$8.90	$8.90
7 purchase totals =	$430.95		$465.2894	$465.29	$465.30	$465.30