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	$236.99	9.662%	$259.888	$259.89	$259.90	$259.90
Purchase #2	$16.85	9.254%	$18.4093	$18.41	$18.40	$18.40
Purchase #3	$38.27	10.718%	$42.3718	$42.37	$42.35	$42.40
Purchase #4	$219.54	11.522%	$244.8354	$244.84	$244.85	$244.80
Purchase #5	$130.98	13.503%	$148.6662	$148.67	$148.65	$148.70
Purchase #6	$29.76	8.661%	$32.3375	$32.34	$32.35	$32.30
Purchase #7	$36.67	5.727%	$38.7701	$38.77	$38.75	$38.80
7 purchase totals =	$709.06		$785.2783	$785.29	$785.25	$785.30