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	$220.31	13.700%	$250.4925	$250.49	$250.50	$250.50
Purchase #2	$167.54	3.455%	$173.3285	$173.33	$173.35	$173.30
Purchase #3	$225.75	5.375%	$237.8841	$237.88	$237.90	$237.90
Purchase #4	$245.96	11.763%	$274.8923	$274.89	$274.90	$274.90
Purchase #5	$71.32	13.687%	$81.0816	$81.08	$81.10	$81.10
Purchase #6	$33.54	13.382%	$38.0283	$38.03	$38.05	$38.00
Purchase #7	$97.56	7.684%	$105.0565	$105.06	$105.05	$105.10
7 purchase totals =	$1,061.98		$1,160.7638	$1,160.76	$1,160.85	$1,160.80