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	$16.40	12.481%	$18.4469	$18.45	$18.45	$18.40
Purchase #2	$100.99	4.262%	$105.2942	$105.29	$105.30	$105.30
Purchase #3	$183.67	3.742%	$190.5429	$190.54	$190.55	$190.50
Purchase #4	$18.27	3.270%	$18.8674	$18.87	$18.85	$18.90
Purchase #5	$135.58	4.430%	$141.5862	$141.59	$141.60	$141.60
Purchase #6	$237.39	10.140%	$261.4613	$261.46	$261.45	$261.50
Purchase #7	$92.60	9.645%	$101.5313	$101.53	$101.55	$101.50
7 purchase totals =	$784.90		$837.7302	$837.73	$837.75	$837.70