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	$111.83	3.697%	$115.9644	$115.96	$115.95	$116.00
Purchase #2	$27.81	11.118%	$30.9019	$30.90	$30.90	$30.90
Purchase #3	$191.88	13.340%	$217.4768	$217.48	$217.50	$217.50
Purchase #4	$130.42	7.711%	$140.4767	$140.48	$140.50	$140.50
Purchase #5	$50.40	12.304%	$56.6012	$56.60	$56.60	$56.60
Purchase #6	$54.69	12.319%	$61.4273	$61.43	$61.45	$61.40
Purchase #7	$250.34	6.240%	$265.9612	$265.96	$265.95	$266.00
7 purchase totals =	$817.37		$888.8095	$888.81	$888.85	$888.90