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	$148.31	7.112%	$158.8578	$158.86	$158.85	$158.90
Purchase #2	$64.69	12.859%	$73.0085	$73.01	$73.00	$73.00
Purchase #3	$28.49	9.791%	$31.2795	$31.28	$31.30	$31.30
Purchase #4	$249.57	10.289%	$275.2483	$275.25	$275.25	$275.20
Purchase #5	$39.60	9.570%	$43.3897	$43.39	$43.40	$43.40
Purchase #6	$127.55	9.138%	$139.2055	$139.21	$139.20	$139.20
Purchase #7	$176.25	12.529%	$198.3324	$198.33	$198.35	$198.30
7 purchase totals =	$834.46		$919.3217	$919.33	$919.35	$919.30