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	$89.73	11.355%	$99.9188	$99.92	$99.90	$99.90
Purchase #2	$196.71	6.594%	$209.6811	$209.68	$209.70	$209.70
Purchase #3	$212.64	12.535%	$239.2944	$239.29	$239.30	$239.30
Purchase #4	$238.46	6.271%	$253.4138	$253.41	$253.40	$253.40
Purchase #5	$139.75	13.429%	$158.517	$158.52	$158.50	$158.50
Purchase #6	$167.48	13.867%	$190.7045	$190.70	$190.70	$190.70
Purchase #7	$55.46	3.431%	$57.3628	$57.36	$57.35	$57.40
7 purchase totals =	$1,100.23		$1,208.8924	$1,208.88	$1,208.85	$1,208.90