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	$44.80	11.340%	$49.8803	$49.88	$49.90	$49.90
Purchase #2	$191.28	4.160%	$199.2372	$199.24	$199.25	$199.20
Purchase #3	$112.44	10.253%	$123.9685	$123.97	$123.95	$124.00
Purchase #4	$85.98	4.705%	$90.0254	$90.03	$90.05	$90.00
Purchase #5	$29.67	5.767%	$31.3811	$31.38	$31.40	$31.40
Purchase #6	$237.29	3.827%	$246.3711	$246.37	$246.35	$246.40
Purchase #7	$104.57	6.618%	$111.4904	$111.49	$111.50	$111.50
7 purchase totals =	$806.03		$852.3540	$852.36	$852.40	$852.40