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	$42.25	7.866%	$45.5734	$45.57	$45.55	$45.60
Purchase #2	$126.51	11.685%	$141.2927	$141.29	$141.30	$141.30
Purchase #3	$24.51	4.498%	$25.6125	$25.61	$25.60	$25.60
Purchase #4	$42.83	8.182%	$46.3344	$46.33	$46.35	$46.30
Purchase #5	$164.79	7.760%	$177.5777	$177.58	$177.60	$177.60
Purchase #6	$97.46	11.758%	$108.9193	$108.92	$108.90	$108.90
Purchase #7	$103.61	8.345%	$112.2563	$112.26	$112.25	$112.30
7 purchase totals =	$601.96		$657.5663	$657.56	$657.55	$657.60