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	$250.39	10.190%	$275.9047	$275.90	$275.90	$275.90
Purchase #2	$101.89	5.347%	$107.3381	$107.34	$107.35	$107.30
Purchase #3	$20.41	5.550%	$21.5428	$21.54	$21.55	$21.50
Purchase #4	$17.42	8.319%	$18.8692	$18.87	$18.85	$18.90
Purchase #5	$89.35	9.238%	$97.6042	$97.60	$97.60	$97.60
Purchase #6	$53.79	9.800%	$59.0614	$59.06	$59.05	$59.10
Purchase #7	$143.30	11.319%	$159.5201	$159.52	$159.50	$159.50
7 purchase totals =	$676.55		$739.8405	$739.83	$739.80	$739.80