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	$88.91	12.292%	$99.8388	$99.84	$99.85	$99.80
Purchase #2	$204.96	9.256%	$223.9311	$223.93	$223.95	$223.90
Purchase #3	$126.56	3.658%	$131.1896	$131.19	$131.20	$131.20
Purchase #4	$17.66	7.746%	$19.0279	$19.03	$19.05	$19.00
Purchase #5	$115.97	13.767%	$131.9356	$131.94	$131.95	$131.90
Purchase #6	$13.98	6.536%	$14.8937	$14.89	$14.90	$14.90
Purchase #7	$26.39	5.618%	$27.8726	$27.87	$27.85	$27.90
7 purchase totals =	$594.43		$648.6893	$648.69	$648.75	$648.60