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	$43.83	6.854%	$46.8341	$46.83	$46.85	$46.80
Purchase #2	$73.80	8.692%	$80.2147	$80.21	$80.20	$80.20
Purchase #3	$54.31	9.549%	$59.4961	$59.50	$59.50	$59.50
Purchase #4	$122.98	12.786%	$138.7042	$138.70	$138.70	$138.70
Purchase #5	$182.33	7.657%	$196.291	$196.29	$196.30	$196.30
Purchase #6	$15.56	8.225%	$16.8398	$16.84	$16.85	$16.80
Purchase #7	$103.75	5.603%	$109.5631	$109.56	$109.55	$109.60
7 purchase totals =	$596.56		$647.9430	$647.93	$647.95	$647.90