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	$237.34	4.859%	$248.8724	$248.87	$248.85	$248.90
Purchase #2	$31.91	3.715%	$33.0955	$33.10	$33.10	$33.10
Purchase #3	$154.26	5.546%	$162.8153	$162.82	$162.80	$162.80
Purchase #4	$84.47	6.533%	$89.9884	$89.99	$90.00	$90.00
Purchase #5	$223.50	8.663%	$242.8618	$242.86	$242.85	$242.90
Purchase #6	$89.60	9.462%	$98.078	$98.08	$98.10	$98.10
Purchase #7	$70.73	13.849%	$80.5254	$80.53	$80.55	$80.50
7 purchase totals =	$891.81		$956.2368	$956.25	$956.25	$956.30