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	$43.31	13.669%	$49.23	$49.23	$49.25	$49.20
Purchase #2	$235.27	9.745%	$258.1971	$258.20	$258.20	$258.20
Purchase #3	$91.63	9.536%	$100.3678	$100.37	$100.35	$100.40
Purchase #4	$99.54	10.369%	$109.8613	$109.86	$109.85	$109.90
Purchase #5	$244.73	5.165%	$257.3703	$257.37	$257.35	$257.40
Purchase #6	$68.46	6.800%	$73.1153	$73.12	$73.10	$73.10
Purchase #7	$119.27	10.309%	$131.5655	$131.57	$131.55	$131.60
7 purchase totals =	$902.21		$979.7073	$979.72	$979.65	$979.80