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	$6.38	5.327%	$6.7199	$6.72	$6.70	$6.70
Purchase #2	$117.41	7.578%	$126.3073	$126.31	$126.30	$126.30
Purchase #3	$104.42	4.522%	$109.1419	$109.14	$109.15	$109.10
Purchase #4	$230.38	3.588%	$238.646	$238.65	$238.65	$238.60
Purchase #5	$181.93	5.421%	$191.7924	$191.79	$191.80	$191.80
Purchase #6	$136.77	6.662%	$145.8816	$145.88	$145.90	$145.90
Purchase #7	$200.42	11.186%	$222.839	$222.84	$222.85	$222.80
7 purchase totals =	$977.71		$1,041.3281	$1,041.33	$1,041.35	$1,041.20