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	$138.39	7.181%	$148.3278	$148.33	$148.35	$148.30
Purchase #2	$133.61	9.396%	$146.164	$146.16	$146.15	$146.20
Purchase #3	$142.89	3.147%	$147.3867	$147.39	$147.40	$147.40
Purchase #4	$67.82	6.870%	$72.4792	$72.48	$72.50	$72.50
Purchase #5	$89.86	5.794%	$95.0665	$95.07	$95.05	$95.10
Purchase #6	$229.53	12.131%	$257.3743	$257.37	$257.35	$257.40
Purchase #7	$24.39	11.387%	$27.1673	$27.17	$27.15	$27.20
7 purchase totals =	$826.49		$893.9658	$893.97	$893.95	$894.10