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	$77.94	6.153%	$82.7356	$82.74	$82.75	$82.70
Purchase #2	$74.27	12.277%	$83.3881	$83.39	$83.40	$83.40
Purchase #3	$74.61	10.613%	$82.5284	$82.53	$82.55	$82.50
Purchase #4	$72.74	6.589%	$77.5328	$77.53	$77.55	$77.50
Purchase #5	$21.28	4.374%	$22.2108	$22.21	$22.20	$22.20
Purchase #6	$138.38	10.479%	$152.8808	$152.88	$152.90	$152.90
Purchase #7	$170.58	9.756%	$187.2218	$187.22	$187.20	$187.20
7 purchase totals =	$629.80		$688.4983	$688.50	$688.55	$688.40