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	$188.45	4.307%	$196.5665	$196.57	$196.55	$196.60
Purchase #2	$95.96	6.537%	$102.2329	$102.23	$102.25	$102.20
Purchase #3	$32.94	9.847%	$36.1836	$36.18	$36.20	$36.20
Purchase #4	$136.42	3.603%	$141.3352	$141.34	$141.35	$141.30
Purchase #5	$70.52	5.272%	$74.2378	$74.24	$74.25	$74.20
Purchase #6	$37.86	11.793%	$42.3248	$42.32	$42.30	$42.30
Purchase #7	$176.55	5.282%	$185.8754	$185.88	$185.90	$185.90
7 purchase totals =	$738.70		$778.7562	$778.76	$778.80	$778.70