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	$40.93	5.158%	$43.0412	$43.04	$43.05	$43.00
Purchase #2	$227.97	8.586%	$247.5435	$247.54	$247.55	$247.50
Purchase #3	$161.60	12.563%	$181.9018	$181.90	$181.90	$181.90
Purchase #4	$55.52	7.246%	$59.543	$59.54	$59.55	$59.50
Purchase #5	$31.69	5.444%	$33.4152	$33.42	$33.40	$33.40
Purchase #6	$148.26	6.326%	$157.6389	$157.64	$157.65	$157.60
Purchase #7	$247.35	10.451%	$273.2005	$273.20	$273.20	$273.20
7 purchase totals =	$913.32		$996.2841	$996.28	$996.30	$996.10