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	$121.56	7.790%	$131.0295	$131.03	$131.05	$131.00
Purchase #2	$14.98	6.494%	$15.9528	$15.95	$15.95	$16.00
Purchase #3	$14.64	5.540%	$15.4511	$15.45	$15.45	$15.50
Purchase #4	$168.94	8.284%	$182.935	$182.94	$182.95	$182.90
Purchase #5	$156.62	10.633%	$173.2734	$173.27	$173.25	$173.30
Purchase #6	$215.97	10.421%	$238.4762	$238.48	$238.50	$238.50
Purchase #7	$226.27	8.648%	$245.8378	$245.84	$245.85	$245.80
7 purchase totals =	$918.98		$1,002.9558	$1,002.96	$1,003.00	$1,003.00