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	$48.31	13.126%	$54.6512	$54.65	$54.65	$54.70
Purchase #2	$162.90	11.869%	$182.2346	$182.23	$182.25	$182.20
Purchase #3	$63.58	5.102%	$66.8239	$66.82	$66.80	$66.80
Purchase #4	$118.70	13.173%	$134.3364	$134.34	$134.35	$134.30
Purchase #5	$204.97	9.729%	$224.9115	$224.91	$224.90	$224.90
Purchase #6	$65.28	10.783%	$72.3191	$72.32	$72.30	$72.30
Purchase #7	$61.81	5.633%	$65.2918	$65.29	$65.30	$65.30
7 purchase totals =	$725.55		$800.5685	$800.56	$800.55	$800.50