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	$85.56	7.393%	$91.8855	$91.89	$91.90	$91.90
Purchase #2	$122.40	12.408%	$137.5874	$137.59	$137.60	$137.60
Purchase #3	$244.25	6.211%	$259.4204	$259.42	$259.40	$259.40
Purchase #4	$18.68	6.415%	$19.8783	$19.88	$19.90	$19.90
Purchase #5	$247.75	4.778%	$259.5875	$259.59	$259.60	$259.60
Purchase #6	$218.41	4.259%	$227.7121	$227.71	$227.70	$227.70
Purchase #7	$175.79	13.856%	$200.1475	$200.15	$200.15	$200.10
7 purchase totals =	$1,112.84		$1,196.2187	$1,196.23	$1,196.25	$1,196.20