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	$228.68	12.399%	$257.034	$257.03	$257.05	$257.00
Purchase #2	$223.51	3.818%	$232.0436	$232.04	$232.05	$232.00
Purchase #3	$128.83	9.497%	$141.065	$141.07	$141.05	$141.10
Purchase #4	$98.25	13.320%	$111.3369	$111.34	$111.35	$111.30
Purchase #5	$31.25	3.105%	$32.2203	$32.22	$32.20	$32.20
Purchase #6	$99.84	9.601%	$109.4256	$109.43	$109.45	$109.40
Purchase #7	$84.91	6.540%	$90.4631	$90.46	$90.45	$90.50
7 purchase totals =	$895.27		$973.5885	$973.59	$973.60	$973.50