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	$160.96	6.189%	$170.9218	$170.92	$170.90	$170.90
Purchase #2	$170.60	11.482%	$190.1883	$190.19	$190.20	$190.20
Purchase #3	$38.71	5.810%	$40.9591	$40.96	$40.95	$41.00
Purchase #4	$179.88	10.144%	$198.127	$198.13	$198.15	$198.10
Purchase #5	$199.48	5.218%	$209.8889	$209.89	$209.90	$209.90
Purchase #6	$80.33	10.669%	$88.9004	$88.90	$88.90	$88.90
Purchase #7	$186.31	10.494%	$205.8614	$205.86	$205.85	$205.90
7 purchase totals =	$1,016.27		$1,104.8469	$1,104.85	$1,104.85	$1,104.90