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	$204.39	8.681%	$222.1331	$222.13	$222.15	$222.10
Purchase #2	$195.93	9.850%	$215.2291	$215.23	$215.25	$215.20
Purchase #3	$95.94	4.102%	$99.8755	$99.88	$99.90	$99.90
Purchase #4	$161.25	3.160%	$166.3455	$166.35	$166.35	$166.30
Purchase #5	$117.84	6.854%	$125.9168	$125.92	$125.90	$125.90
Purchase #6	$209.45	12.129%	$234.8542	$234.85	$234.85	$234.90
Purchase #7	$187.55	11.531%	$209.1764	$209.18	$209.20	$209.20
7 purchase totals =	$1,172.35		$1,273.5306	$1,273.54	$1,273.60	$1,273.50