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	$136.49	3.695%	$141.5333	$141.53	$141.55	$141.50
Purchase #2	$97.41	8.225%	$105.422	$105.42	$105.40	$105.40
Purchase #3	$19.28	12.442%	$21.6788	$21.68	$21.70	$21.70
Purchase #4	$200.44	7.589%	$215.6514	$215.65	$215.65	$215.70
Purchase #5	$81.37	10.730%	$90.101	$90.10	$90.10	$90.10
Purchase #6	$207.94	11.514%	$231.8822	$231.88	$231.90	$231.90
Purchase #7	$57.40	3.507%	$59.413	$59.41	$59.40	$59.40
7 purchase totals =	$800.33		$865.6817	$865.67	$865.70	$865.70