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	$169.79	8.241%	$183.7824	$183.78	$183.80	$183.80
Purchase #2	$222.74	8.759%	$242.2498	$242.25	$242.25	$242.20
Purchase #3	$39.85	6.504%	$42.4418	$42.44	$42.45	$42.40
Purchase #4	$78.50	6.168%	$83.3419	$83.34	$83.35	$83.30
Purchase #5	$176.83	7.866%	$190.7394	$190.74	$190.75	$190.70
Purchase #6	$85.83	6.644%	$91.5325	$91.53	$91.55	$91.50
Purchase #7	$96.86	7.765%	$104.3812	$104.38	$104.40	$104.40
7 purchase totals =	$870.40		$938.4690	$938.46	$938.55	$938.30