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	$82.91	10.142%	$91.3187	$91.32	$91.30	$91.30
Purchase #2	$137.55	7.254%	$147.5279	$147.53	$147.55	$147.50
Purchase #3	$205.63	6.769%	$219.5491	$219.55	$219.55	$219.50
Purchase #4	$56.81	12.262%	$63.776	$63.78	$63.80	$63.80
Purchase #5	$15.34	4.376%	$16.0113	$16.01	$16.00	$16.00
Purchase #6	$104.78	6.315%	$111.3969	$111.40	$111.40	$111.40
Purchase #7	$35.67	7.302%	$38.2746	$38.27	$38.25	$38.30
7 purchase totals =	$638.69		$687.8545	$687.86	$687.85	$687.80