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	$20.93	4.291%	$21.8281	$21.83	$21.85	$21.80
Purchase #2	$215.29	3.235%	$222.2546	$222.25	$222.25	$222.30
Purchase #3	$25.38	12.524%	$28.5586	$28.56	$28.55	$28.60
Purchase #4	$232.71	5.558%	$245.644	$245.64	$245.65	$245.60
Purchase #5	$108.32	11.494%	$120.7703	$120.77	$120.75	$120.80
Purchase #6	$52.73	8.631%	$57.2811	$57.28	$57.30	$57.30
Purchase #7	$194.86	12.870%	$219.9385	$219.94	$219.95	$219.90
7 purchase totals =	$850.22		$916.2752	$916.27	$916.30	$916.30