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	$222.88	11.492%	$248.4934	$248.49	$248.50	$248.50
Purchase #2	$109.92	6.317%	$116.8636	$116.86	$116.85	$116.90
Purchase #3	$134.68	9.273%	$147.1689	$147.17	$147.15	$147.20
Purchase #4	$65.84	10.196%	$72.553	$72.55	$72.55	$72.60
Purchase #5	$148.51	11.416%	$165.4639	$165.46	$165.45	$165.50
Purchase #6	$125.33	11.384%	$139.5976	$139.60	$139.60	$139.60
Purchase #7	$188.60	11.498%	$210.2852	$210.29	$210.30	$210.30
7 purchase totals =	$995.76		$1,100.4256	$1,100.42	$1,100.40	$1,100.60