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	$82.88	8.334%	$89.7872	$89.79	$89.80	$89.80
Purchase #2	$89.30	10.630%	$98.7926	$98.79	$98.80	$98.80
Purchase #3	$248.64	3.471%	$257.2703	$257.27	$257.25	$257.30
Purchase #4	$232.57	13.507%	$263.9832	$263.98	$264.00	$264.00
Purchase #5	$7.43	6.706%	$7.9283	$7.93	$7.95	$7.90
Purchase #6	$20.36	6.308%	$21.6443	$21.64	$21.65	$21.60
Purchase #7	$209.66	13.553%	$238.0752	$238.08	$238.10	$238.10
7 purchase totals =	$890.84		$977.4811	$977.48	$977.55	$977.50