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	$131.69	5.836%	$139.3754	$139.38	$139.40	$139.40
Purchase #2	$248.79	6.212%	$264.2448	$264.24	$264.25	$264.20
Purchase #3	$111.34	3.354%	$115.0743	$115.07	$115.05	$115.10
Purchase #4	$52.83	12.792%	$59.588	$59.59	$59.60	$59.60
Purchase #5	$31.46	8.326%	$34.0794	$34.08	$34.10	$34.10
Purchase #6	$145.62	7.515%	$156.5633	$156.56	$156.55	$156.60
Purchase #7	$200.57	8.674%	$217.9674	$217.97	$217.95	$218.00
7 purchase totals =	$922.30		$986.8926	$986.89	$986.90	$987.00