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	$104.64	4.357%	$109.1992	$109.20	$109.20	$109.20
Purchase #2	$243.61	9.746%	$267.3522	$267.35	$267.35	$267.40
Purchase #3	$49.50	13.391%	$56.1285	$56.13	$56.15	$56.10
Purchase #4	$91.30	5.314%	$96.1517	$96.15	$96.15	$96.20
Purchase #5	$86.53	4.728%	$90.6211	$90.62	$90.60	$90.60
Purchase #6	$118.83	6.366%	$126.3947	$126.39	$126.40	$126.40
Purchase #7	$181.86	5.354%	$191.5968	$191.60	$191.60	$191.60
7 purchase totals =	$876.27		$937.4442	$937.44	$937.45	$937.50