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	$37.56	6.318%	$39.933	$39.93	$39.95	$39.90
Purchase #2	$164.91	12.671%	$185.8057	$185.81	$185.80	$185.80
Purchase #3	$224.72	4.380%	$234.5627	$234.56	$234.55	$234.60
Purchase #4	$103.75	10.427%	$114.568	$114.57	$114.55	$114.60
Purchase #5	$146.77	3.742%	$152.2621	$152.26	$152.25	$152.30
Purchase #6	$98.32	6.427%	$104.639	$104.64	$104.65	$104.60
Purchase #7	$241.44	7.483%	$259.507	$259.51	$259.50	$259.50
7 purchase totals =	$1,017.47		$1,091.2775	$1,091.28	$1,091.25	$1,091.30