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	$37.33	7.172%	$40.0073	$40.01	$40.00	$40.00
Purchase #2	$151.79	8.462%	$164.6345	$164.63	$164.65	$164.60
Purchase #3	$168.78	8.107%	$182.463	$182.46	$182.45	$182.50
Purchase #4	$215.54	10.153%	$237.4238	$237.42	$237.40	$237.40
Purchase #5	$32.46	3.484%	$33.5909	$33.59	$33.60	$33.60
Purchase #6	$191.37	10.459%	$211.3854	$211.39	$211.40	$211.40
Purchase #7	$39.60	5.512%	$41.7828	$41.78	$41.80	$41.80
7 purchase totals =	$836.87		$911.2877	$911.28	$911.30	$911.30