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	$40.32	6.218%	$42.8271	$42.83	$42.85	$42.80
Purchase #2	$170.30	4.193%	$177.4407	$177.44	$177.45	$177.40
Purchase #3	$129.88	10.359%	$143.3343	$143.33	$143.35	$143.30
Purchase #4	$106.44	13.144%	$120.4305	$120.43	$120.45	$120.40
Purchase #5	$98.35	4.584%	$102.8584	$102.86	$102.85	$102.90
Purchase #6	$144.77	4.521%	$151.3151	$151.32	$151.30	$151.30
Purchase #7	$79.66	3.743%	$82.6417	$82.64	$82.65	$82.60
7 purchase totals =	$769.72		$820.8478	$820.85	$820.90	$820.70