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	$223.66	11.470%	$249.3138	$249.31	$249.30	$249.30
Purchase #2	$99.81	10.105%	$109.8958	$109.90	$109.90	$109.90
Purchase #3	$9.94	5.760%	$10.5125	$10.51	$10.50	$10.50
Purchase #4	$118.91	4.379%	$124.1171	$124.12	$124.10	$124.10
Purchase #5	$161.81	5.602%	$170.8746	$170.87	$170.85	$170.90
Purchase #6	$250.47	13.137%	$283.3742	$283.37	$283.35	$283.40
Purchase #7	$85.96	4.673%	$89.9769	$89.98	$90.00	$90.00
7 purchase totals =	$950.56		$1,038.0649	$1,038.06	$1,038.00	$1,038.10