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	$189.57	11.769%	$211.8805	$211.88	$211.90	$211.90
Purchase #2	$212.51	12.616%	$239.3203	$239.32	$239.30	$239.30
Purchase #3	$112.82	12.853%	$127.3208	$127.32	$127.30	$127.30
Purchase #4	$174.85	7.170%	$187.3867	$187.39	$187.40	$187.40
Purchase #5	$76.49	6.625%	$81.5575	$81.56	$81.55	$81.60
Purchase #6	$108.31	7.797%	$116.7549	$116.75	$116.75	$116.80
Purchase #7	$146.74	8.273%	$158.8798	$158.88	$158.90	$158.90
7 purchase totals =	$1,021.29		$1,123.1005	$1,123.10	$1,123.10	$1,123.20