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	$117.59	12.849%	$132.6991	$132.70	$132.70	$132.70
Purchase #2	$95.52	7.191%	$102.3888	$102.39	$102.40	$102.40
Purchase #3	$184.82	6.780%	$197.3508	$197.35	$197.35	$197.40
Purchase #4	$147.36	6.239%	$156.5538	$156.55	$156.55	$156.60
Purchase #5	$96.28	7.519%	$103.5193	$103.52	$103.50	$103.50
Purchase #6	$245.59	13.771%	$279.4102	$279.41	$279.40	$279.40
Purchase #7	$68.83	13.777%	$78.3127	$78.31	$78.30	$78.30
7 purchase totals =	$955.99		$1,050.2347	$1,050.23	$1,050.20	$1,050.30