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	$155.32	12.228%	$174.3125	$174.31	$174.30	$174.30
Purchase #2	$80.61	12.651%	$90.808	$90.81	$90.80	$90.80
Purchase #3	$20.55	3.342%	$21.2368	$21.24	$21.25	$21.20
Purchase #4	$107.26	8.410%	$116.2806	$116.28	$116.30	$116.30
Purchase #5	$143.60	12.728%	$161.8774	$161.88	$161.90	$161.90
Purchase #6	$29.30	6.524%	$31.2115	$31.21	$31.20	$31.20
Purchase #7	$170.34	8.345%	$184.5549	$184.55	$184.55	$184.60
7 purchase totals =	$706.98		$780.2817	$780.28	$780.30	$780.30