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	$204.52	12.105%	$229.2771	$229.28	$229.30	$229.30
Purchase #2	$129.38	10.274%	$142.6725	$142.67	$142.65	$142.70
Purchase #3	$134.38	6.633%	$143.2934	$143.29	$143.30	$143.30
Purchase #4	$181.28	4.574%	$189.5717	$189.57	$189.55	$189.60
Purchase #5	$143.90	5.846%	$152.3124	$152.31	$152.30	$152.30
Purchase #6	$134.43	4.544%	$140.5385	$140.54	$140.55	$140.50
Purchase #7	$215.30	12.567%	$242.3568	$242.36	$242.35	$242.40
7 purchase totals =	$1,143.19		$1,240.0224	$1,240.02	$1,240.00	$1,240.10