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	$99.25	12.398%	$111.555	$111.56	$111.55	$111.60
Purchase #2	$42.31	3.293%	$43.7033	$43.70	$43.70	$43.70
Purchase #3	$161.27	6.310%	$171.4461	$171.45	$171.45	$171.40
Purchase #4	$37.66	8.556%	$40.8822	$40.88	$40.90	$40.90
Purchase #5	$176.48	7.453%	$189.6331	$189.63	$189.65	$189.60
Purchase #6	$69.25	7.260%	$74.2776	$74.28	$74.30	$74.30
Purchase #7	$125.49	10.865%	$139.1245	$139.12	$139.10	$139.10
7 purchase totals =	$711.71		$770.6218	$770.62	$770.65	$770.60