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	$141.80	4.171%	$147.7145	$147.71	$147.70	$147.70
Purchase #2	$94.48	3.806%	$98.0759	$98.08	$98.10	$98.10
Purchase #3	$221.92	7.444%	$238.4397	$238.44	$238.45	$238.40
Purchase #4	$65.81	13.825%	$74.9082	$74.91	$74.90	$74.90
Purchase #5	$75.74	3.175%	$78.1447	$78.14	$78.15	$78.10
Purchase #6	$123.88	6.464%	$131.8876	$131.89	$131.90	$131.90
Purchase #7	$44.37	11.643%	$49.536	$49.54	$49.55	$49.50
7 purchase totals =	$768.00		$818.7066	$818.71	$818.75	$818.60