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	$19.89	3.682%	$20.6223	$20.62	$20.60	$20.60
Purchase #2	$242.79	12.567%	$273.3014	$273.30	$273.30	$273.30
Purchase #3	$121.68	9.759%	$133.5548	$133.55	$133.55	$133.60
Purchase #4	$213.31	4.228%	$222.3287	$222.33	$222.35	$222.30
Purchase #5	$134.70	7.375%	$144.6341	$144.63	$144.65	$144.60
Purchase #6	$207.54	12.666%	$233.827	$233.83	$233.85	$233.80
Purchase #7	$133.36	5.520%	$140.7215	$140.72	$140.70	$140.70
7 purchase totals =	$1,073.27		$1,168.9898	$1,168.98	$1,169.00	$1,168.90