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	$150.25	13.516%	$170.5578	$170.56	$170.55	$170.60
Purchase #2	$17.39	5.415%	$18.3317	$18.33	$18.35	$18.30
Purchase #3	$36.47	12.608%	$41.0681	$41.07	$41.05	$41.10
Purchase #4	$68.39	4.247%	$71.2945	$71.29	$71.30	$71.30
Purchase #5	$80.60	12.686%	$90.8249	$90.82	$90.80	$90.80
Purchase #6	$27.58	4.249%	$28.7519	$28.75	$28.75	$28.80
Purchase #7	$232.81	13.639%	$264.563	$264.56	$264.55	$264.60
7 purchase totals =	$613.49		$685.3919	$685.38	$685.35	$685.50