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	$31.78	13.726%	$36.1421	$36.14	$36.15	$36.10
Purchase #2	$84.31	6.715%	$89.9714	$89.97	$89.95	$90.00
Purchase #3	$211.25	6.856%	$225.7333	$225.73	$225.75	$225.70
Purchase #4	$156.52	7.583%	$168.3889	$168.39	$168.40	$168.40
Purchase #5	$80.28	5.711%	$84.8648	$84.86	$84.85	$84.90
Purchase #6	$42.44	6.121%	$45.0378	$45.04	$45.05	$45.00
Purchase #7	$115.94	6.658%	$123.6593	$123.66	$123.65	$123.70
7 purchase totals =	$722.52		$773.7976	$773.79	$773.80	$773.80