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	$79.40	11.654%	$88.6533	$88.65	$88.65	$88.70
Purchase #2	$136.61	8.693%	$148.4855	$148.49	$148.50	$148.50
Purchase #3	$219.67	5.162%	$231.0094	$231.01	$231.00	$231.00
Purchase #4	$93.94	5.680%	$99.2758	$99.28	$99.30	$99.30
Purchase #5	$235.28	10.191%	$259.2574	$259.26	$259.25	$259.30
Purchase #6	$66.94	8.279%	$72.482	$72.48	$72.50	$72.50
Purchase #7	$134.25	6.326%	$142.7427	$142.74	$142.75	$142.70
7 purchase totals =	$966.09		$1,041.9061	$1,041.91	$1,041.95	$1,042.00