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	$215.63	4.618%	$225.5878	$225.59	$225.60	$225.60
Purchase #2	$32.85	12.387%	$36.9191	$36.92	$36.90	$36.90
Purchase #3	$225.25	7.627%	$242.4298	$242.43	$242.45	$242.40
Purchase #4	$94.37	11.835%	$105.5387	$105.54	$105.55	$105.50
Purchase #5	$155.61	8.385%	$168.6579	$168.66	$168.65	$168.70
Purchase #6	$33.90	12.835%	$38.2511	$38.25	$38.25	$38.30
Purchase #7	$78.79	5.234%	$82.9139	$82.91	$82.90	$82.90
7 purchase totals =	$836.40		$900.2983	$900.30	$900.30	$900.30