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	$137.86	9.847%	$151.4351	$151.44	$151.45	$151.40
Purchase #2	$84.32	6.231%	$89.574	$89.57	$89.55	$89.60
Purchase #3	$70.25	13.502%	$79.7352	$79.74	$79.75	$79.70
Purchase #4	$94.82	10.834%	$105.0928	$105.09	$105.10	$105.10
Purchase #5	$82.28	8.417%	$89.2055	$89.21	$89.20	$89.20
Purchase #6	$195.63	12.574%	$220.2285	$220.23	$220.25	$220.20
Purchase #7	$81.86	13.214%	$92.677	$92.68	$92.70	$92.70
7 purchase totals =	$747.02		$827.9481	$827.96	$828.00	$827.90