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	$30.37	10.380%	$33.5224	$33.52	$33.50	$33.50
Purchase #2	$88.83	11.249%	$98.8225	$98.82	$98.80	$98.80
Purchase #3	$43.43	13.728%	$49.3921	$49.39	$49.40	$49.40
Purchase #4	$233.95	5.655%	$247.1799	$247.18	$247.20	$247.20
Purchase #5	$165.79	11.483%	$184.8277	$184.83	$184.85	$184.80
Purchase #6	$130.44	8.167%	$141.093	$141.09	$141.10	$141.10
Purchase #7	$118.67	7.758%	$127.8764	$127.88	$127.90	$127.90
7 purchase totals =	$811.48		$882.7140	$882.71	$882.75	$882.70